Thomas is an avid weather enthusiast, landscaper and organic gardener. This blog is dedicated to Northeast and tropical weather forecasting. Enjoy!
By: sullivanweather, 6:51 AM GMT on November 29, 2008
Current watches, warnings and advisories.
Synopsis - Issued 11/29 @1:45am
Weak high pressure builds over the Northeast on Saturday, providing a fair day for most outside of a few lake effect flurries. On Sunday, a complex double-barrel low pressure system will develop over the Southeast and push towards the region bringing widespread rain to the coast, with a mix or snow to the interior lasting into Monday. It will be fair for Tuesday and most of Wednesday before a strong cold front brings a return to winter-like weather by Thursday.
Near-term - Issued 11/29 @1:45am
Very localized heavy lake effect snow will be winding down across the Tug Hill Plateau during the overnight and into the early morning hours on Saturday. Several more inches of snow may accumulate on top of the quick 4-8” burst seen Friday afternoon/evening. A few snow showers have also pushed off Lake Erie into central New York but these will leave a dusting at most. Temperatures will begin the day in the 20’s across the interior with 30’s along the coastal plain.
Short-term - Issued 11/29 @1:45am
With high pressure, albeit weak, building over the region on Saturday there should be fair skies for most with light and variable breezes. High temperatures will be tolerable, with highs in the 30’s across the interior and 40’s along the coastal plain, right on cue for the end of November. High clouds will begin to filter in from the south during the late afternoon and evening hours, thickening and lowering during the overnight. A few light flurries (interior) and sprinkles (coast) should cross the Mason-Dixon line after midnight but should remain confined to south of the I-78 corridor. Lows will be in the teens and 20’s across the north with upper 20’s to mid 30’s across the south and along the immediate coast. Winds will begin to shift from the east around 5-10mph.
A very complex set up on Sunday thanks to a series of disturbances dropping into the upper trough over the Mississippi Valley region. This will help to sharpen and deepen the trough over the Mid-Mississippi Valley region as the northern stream disturbances provide support for cyclogenesis over the Tennessee Valley. In addition, several areas of low pressure will develop along a quasi-stationary boundary aligned from the Florida panhandle to the Outer Banks of North Carolina, as they fight to become the secondary low. In response to this deepening trough, heights will build over the western Atlantic with a strong southwesterly jet developing over the eastern US helping to transport moist, mild southerly air up the coast. The aforementioned weak high pressure that will bring fair weather to the region on Saturday won’t put up much of a fight to the advancing low as it marches northeastwards, meaning the cold air over the region now will be transient in nature. Initial batch of precipitation will overspread most of Pennsylvania, New Jersey, the southern half of New York and southern New England during the day on Sunday thanks to strong theta-e advection. Across most of the interior above 1,000’, temperatures aloft and in the boundary layer, as well as partial thicknesses, indicate that precipitation type will be in the form of snow. At lower elevations rain will mix in with the snow as the boundary layer warms into the mid and upper 30’s. There’s a low threat for freezing rain in some of the deeper valleys of central Pennsylvania, right along the east side of the Appalachians. However, without any sufficient cold air source, this looks to be isolated at best. Along the coastal plain rain should be the dominant precipitation type, although there may be a few sleet pellets at the onset given the large dewpoint depressions. It will be a cold raw rain, with temperatures hovering around the 40°F mark. The first batch of precipitation won’t be terribly heavy or steady, with about a quarter to a third of an inch expected. Where this falls as snow an inch or two, possibly three, will coat mainly the cold/grassy/snow covered surfaces. Surface ridge axis over northern New York and New England should keep these areas dry but clouds will thicken as the day progresses, limiting sunshine. Across the north highs will be within a few degrees of freezing.
The entire double(triple?)-barrel mess moves into the Northeast Sunday night into Monday. This is where it gets even more complicated. Neither low looks to take over, sharing energy equally amongst themselves and remaining broad. Convection off the coast associated with the coastal front interacting with the Gulf Stream may help to keep lower pressure just offshore, tending to pull the coastal east, even though the trough axis is displaced rather far to the west. Owning to this far west upper trough axis will be the primary low, moving towards the west end of Lake Erie. Since this system is so broad, with the low pressure centers of the double barrel complex being nearly 600 miles apart and very little baroclinic energy for it to feed off of, there won’t be any major intensification of either low, with both hovering in the mid-990mb range. The center of the 850/700mb low tracks will also be up the west side of the Appalachians and without any high pressure to lock in the cold air over the Northeast, mild air will overspread the region, changing much of the snow over to a mix or rain. The regions that do remain all snow will be confined to the Adirondacks and northern Green/White mountains in northern Vermont and New Hampshire and northwestern Maine. There may be a period of significant sleet and freezing rain across northeast Pennsylvania, the Catskills, Berkshires and Mohawk Valley region as 850mb temperatures rise to 2-3°C overnight but the boundary layer remains near freezing or slightly below. Elsewhere to the south, precipitation will be in the form of rain. There may be a slow rise in temperatures during the night, but ageostrophic flow across the icing threat areas should keep temps at critical level. Along the coastal plain temperatures should be in the 40’s with 20’s across the far north along the Canadian border.
Mid-term - Issued 11/29 @1:45am
Milder air floods into New England on Monday as the snow to mix to rain scenario occurs across the interior. To the west, a cold front moves through New York and Pennsylvania, reaching western New England by evening. Behind this front and leftover rain will change over to snow as strong cold air advection blasts in. Southwesterly flow behind the front will bring lake effect to the Niagara Frontier and the St.Lawrence Valley. Temperatures will remains steady or slowly fall into the 30’s behind the front, with 40’s along the coast. Across New England, temperatures will rise into the 40’s, with 30’s confined to the far north.
Upper trough axis remains over the region on Tuesday. Winds will back to more of a westerly direction with lake bands dropping south and snow showers and/or flurries spreading over the interior as lapse rates increase during diurnal heating in a moist, cyclonic flow regime. Temperatures will fall below normal.
Long-term - Issued 11/29 @1:45am
Next system of concern moves in late Wednesday and early Thursday. A negatively tilting upper trough will approach with a strong cold front along its flanks. This front has anafront characteristics in the models thus far and should bring a rain to snow shower event for most and could drop a couple inches across the interior. Temperatures will climb above normal ahead of this front but drop sharply behind it, to 5-10 degrees below normal. Lake effect snow regime becomes established once again to close out the week with a continuation of much below normal temperatures into next weekend. We may also be dealing with another winter storm by next weekend, if current model trends hold.
Radar: Northeast Region Loop
2008-09 Winter Forecast
Updated: 4:25 PM GMT on December 01, 2008
By: sullivanweather, 9:20 AM GMT on November 27, 2008
Current watches, warnings and advisories.
Synopsis - Issued 11/27 @4:20am
Lake enhanced snow showers will linger through Thanksgiving as the pesky upper low that has brought unsettled weather to the Northeast over the last several days slowly rotates north towards Hudson Bay. A weak clipper blows by the region on Black Friday with light showery precipitation mainly confined to the North Country then a possible winter storm will move up the Eastern Seaboard as a deep trough carves out over the Ohio Valley late this weekend into early next week.
Short-term - Issued 11/27 @4:20am
Vertically stacked low pressure over southern Ontario will finally begin to move north today, away from the Northeast, but we will still feel some of the fringe effects of this system as lake enhanced snow showers continue across upstate New York in cold, moist cyclonic flow. Areas in and around the Adirondacks and St.Lawrence River Valley/Thousand Island region remain under lake effect snow warnings/advisories as anywhere from 3-10 inches of snow can be expected between the time of this writing and late tonight. The Niagara Frontier will also see some lake enhanced snow showers but accumulations will be much lighter, on the order of an inch or two, as deeper moisture has left this region and the air aloft warms, reducing lake induced instabilities. Additional flurries and snow showers extend over central New York and north-central Pennsylvania but these won’t amount to anything more than a dusting and should end by the late morning. Elsewhere across the region skies will be party to mostly clouds, meaning that there will be some periods of sunshine for the first time in many days for some areas. Temperatures will still run near to slightly below normal. Highs will range from the 30’s across the interior, with 40’s across the interior river valleys, such as the Hudson, Susquehanna and Connecticut, as well as along the coastal plain. A few locations may even may the low 50’s across southern New Jersey and extreme southeastern Pennsylvania around the Philadelphia area. Winds will be out of the west to west-southwest around 5-10mph.
Lake effect winds down tonight across upstate New York as the remainder of the region stays dry. High clouds will increase after midnight as a fairly weak clipper system drops down out of the Great Lakes region towards the Northeast. Lows will fall into the 20’s across the north, with a few teens in the higher terrain, with 30’s along the coastal plain. Winds will be generally under 5mph.
Aforementioned clipper low slides through the Northeast on Black Friday, bringing nothing more than an increase in mid/high clouds and perhaps a few snow showers to the higher terrain of northern New York and New England. Once again, temperatures will be seasonal, with highs ranging from the 30’s across the north with 40’s across the southern interior and New England coastal plain. From the New York City metropolitan area on south across the I-95 corridor temperatures should crack the 50°F mark once again. Winds will be from a southerly direction at 5-10mph, shifting from the west after an afternoon cold frontal passage around the same speeds.
The moisture-starved clipper is finally able to tap into some Atlantic moisture that could bring an inch or so of snow across Downeast Maine Friday night. A few snow showers may come off the lakes as weak cold air advection drops 850mb temps down to –6 to –8°C, creating marginal/conditional lake instability parameters, but these won’t amount to much. The remainder of the region will see partly cloudy skies. Lows will range from the 20’s across the interior to the 30’s along the coastal plain.
The clipper will be pulling out to sea by Saturday morning, leaving behind fair skies and a continuation of seasonable temperatures. A couple nuisance flurries will dot the Tug Hill Plateau/Adirondacks region but these won’t amount to anything.
Mid-term - Issued 11/27 @4:20am
Lots of uncertainty in the mid-term as a complex interaction of northern and southern stream disturbances will make for a very challenging forecast. Models do agree that there will be some level of phasing between the two branches of the jet, which will ultimately lead to cyclogenesis somewhere across the Southeast, as the northern stream branch of the jet buckles into a deep trough over the Mississippi/Tennessee Valley. What track the low takes from there is where the models are at odds with each other. The GFS is showing more of an inland runner due to a deeper trough and greater phasing, with the rain/snow line pushing into the interior. On the other hand, the ECMWF, GGEM, UKMET models show less phasing and an offshore track to the low pressure. This puts the rain/snow line much further southeast, bringing more snow to the interior, although QPF is much less than the GFS. Bottom line is that a storm will be affecting at least the southern half of the region to close out the holiday weekend and any traveling plans may need to be pushed up a day to Saturday to avoid delays, especially across the interior. Low pressure moves into New England on Monday with the upper trough axis swinging through keeping unsettled weather over the Northeast. Temperatures will return back to slightly below seasonal averages for late November.
Long-term - Issued 11/27 @4:20am
In the long term, the GFS lifts out the trough, bringing a moderating trend to the region on Tuesday and Wednesday before a cold front blasts through the region on Thursday bringing much colder air back over the Northeast for Friday into next weekend. This solution has little support from other global models, which lingers the trough over the region, keeping the cooler air locked over the Northeast. In addition, a clipper system is progged to drop down from Canada by the GGEM/ECMWF, reaching the Northeast by Wednesday bringing renewed chances for snow across the interior and rain to the coastal plain. In fact, both of these models maintain an active storm track across the eastern US the second half of next week into next weekend with plenty of cold air around for wintry precipitation types. Since the models have shown very little consensus beyond next Tuesday I’ll forego mentioning any individual systems until better run to run consistency develops.
Radar: Northeast Region Loop
2008-09 Winter Forecast
By: sullivanweather, 1:35 PM GMT on November 24, 2008
Current watches, warnings and advisories.
Forecast Discussion - Issued 11/24 @8:35am
It’s Thanksgiving week and I promise to try and provide all the trimmings on this very complicated forecast, considering the implications the adverse weather will have on travel plans. A digging mid/upper trough will tilt negative and slow as it approaches the Northeast, eventually cutting off from the main flow and forming a complex area of low pressure that will unfold into a traveling nightmare. This will be especially true across New England where a strong blocking high located along the Labrador Coast will stop low pressure in its tracks while stalling the frontal boundary and keeping a steady flow of Atlantic moisture poised right over the region through Wednesday. The whole mess should clear the region by Thanksgiving leaving just a few spotty snow showers around the Lakes.
Mid and high level cloudiness are already streaming into the Northeast ahead of the oncoming low pressure center, currently located near Chicago, Illinois, embedded within the 500mb trough. At the surface, ~1030mb high pressure is retreating offshore the New England Coast and will move northeast towards the Canadian Maritimes where it will stall given the North Atlantic blocking in place and slow the forward progress of the approaching low. Some light flurries may be seen from the weak isentropic lift associated with the initial batch of warm air advection currently pushing into the region this morning over the northern mountains. Otherwise partly to mostly cloudy skies will greet the day. Temperatures have been running on the chilly side this morning but are still some 5-10 degrees warmer than yesterday morning given the cloud cover. Temperatures will be in the teens across most of the interior with 20’s in the major river valleys and along the coastal plain.
Clouds continue to filter into the region today, lowering and thickening as the day progresses. Rain will enter western New York and Pennsylvania around the noon hour as the main batch of isentropic lift reaches the area out ahead of the approaching low and associated frontal boundary. Across the higher terrain of the Laurel Highlands and Allegheny Front precipitation should begin as snow, mainly at elevations above 1,400’. Snow levels lower to around 1,000’ across the southerntier of New York State, deeper in the residual cold airmass. Several inches of accumulation should occur across the highest peaks above 1,800’. Leading edge of the precipitation should be lined up with the I-81 corridor by dusk, steadily pushing east where the situation becomes much more tricky during the overnight. With the southerly flow of air between the departing high and approaching low, temperatures will be comparatively mild to days previous, although they will merely climb to what is normal for late November. High will reach into the 40’s along the coastal plain with 30’s expected across much of the interior. A few spot 28-29°F readings may still be found across the higher terrain of northern New York and New England. Wind will increase out of a southerly direction around 10-15mph.
It all starts to go downhill tonight as the precipitation pushes into eastern New York and western New England. Low pressure will have already cut-off 850/700/500mb low pressure centers as the entire upper trough takes on a negative tilt as it drops into the lower Great Lakes region. A strengthening low level jet of 50kts by midnight will start to tap into Atlantic moisture, greatly enhancing precipitation rates all points east of the I-81 corridor. At the surface, low pressure will remain stacked under the mid/upper level low pressure centers, but the surface cold front will occlude and a secondary wave of low pressure will form along the triple point near the Jersey Shore, further aiding in enhancing precipitation rates. Along the coastal plain temperatures will be sufficiently mild enough at the surface and aloft for an all-liquid precipitation event. However, across the interior is where the situation gets quite tricky. Temperatures aloft will initially be cold enough for snow but boundary layer temperatures will be somewhat problematic, especially in the valley locations. Temperatures will have climbed into the upper 30’s to low 40’s during the daylight hours and won’t drop much after dusk with the thick cloud cover overhead. However, a dry airmass will also be in place before the precipitation arrives and temperatures will likely wet-bulb down a couple of degrees once it commences. At the same time, mild air aloft will be carried inland on the increasingly strong low-level jet. This makes the precipitation type forecast very complicated but I’ll give it my best shot. From the northern Poconos, western Catskills, southern Adirondacks and northern Green mountains, precipitation should remain in the form of snow throughout much of the event as temperatures aloft and in the boundary layer appear to be marginally cold enough for snow (more so towards the Adirondacks). The eastern Catskills, Litchfield Hills of Connecticut, Berkshires and southern Green mountains, along with the mid and upper Hudson Valley regions, precipitation should begin as snow during the evening hours. However, as warmer air aloft begins to rocket into the region on a strong south-southeasterly low level jet, precipitation will start to changeover to rain from southeast to northwest. Some of the colder sheltered valley locations across the North Country may also see a period of freezing rain, but these areas look to be isolated, as most areas will also see above freezing boundary layer temperatures. Back towards the west over central/western New York and Pennsylvania the cold front will have pushed east, changing any leftover precipitation over to snow. Here the snow will be showery in nature behind the front as the region gets dry-slotted and shouldn’t add up to much more than an inch or two during the overnight. The big winners tonight will be the elevated terrain (1,400’ and higher) of the western Catskills and southern Adirondacks where up to 6” or more of heavy wet snow may fall. In areas that experience a changeover, snowfall of 1-4” may occur before precipitation turns to rain or a mix. Temperatures across much of the region will be in the 30’s. Exceptions are along the southern New England coastal region where rising temperatures overnight thanks to the strong onshore flow will bring 40’s to the region and across Maine where temperatures should dip into the 20’s. Winds will increase out of the south to southeast at 10-20mph ahead of the frontal boundary and turn towards the west behind it at 5-15mph.
Focus continues to shift east on Tuesday as the axis of precipitation moves into New England. Unrelenting high pressure over the Labrador Coast will be unyielding to the advancing area of low pressure, greatly increasing the frontogenic forcing within this band. There also continues to be great left exit jet dynamics and strong mid/upper level divergence all the while a screaming 60-80kt low level jet from the sub-tropics lifts copious amounts of moisture over New England as strong PVA punches into the region thanks to a lobe of mid-level energy rounding the base of the cut-off. This all spells a heavy precipitation event over New England that should amount to well over an inch of QPF. Areas of upslope enhancement thanks to the strong southeasterly flow should easily see over two inches of QPF. Precipitation-type will be an ongoing concern as the strong surge of moist, mild, maritime air pushes far to the north, eventually overspreading much of Vermont, New Hampshire and western Maine, pushing the 0°C isotherm @850mb into southern Canada. Before this occurs several inches of heavy wet snow may fall over the higher terrain of the Greens, Whites and Presidential Range. Combined with the strong winds, near blizzard conditions will be seen for a short white and the weight of the snow plastered against everything will make trees susceptible to damage, resulting in minor power outages. A few locations that are the last to see a changeover could very well end up with close to a foot of snow. In and around the valley locales any snow accumulations will be much lighter, generally under 3” before a changeover occurs. A few of the more sheltered locations may see a period of freezing rain as well, but this should be short lived as strong southeasterly flow should eventually mix out most of the colder boundary layer air. To the west, the cold front that had been slowly marching through New York and Pennsylvania during the overnight will greatly slow its forward progress upon reaching the Hudson Valley and begin to take on the same southeast to northwest tilt as the entire upper trough. The dry slot, moving in tandem with the cold front, should end the steady precipitation across the remainder of Pennsylvania, as well as much of central and southeastern New York by the afternoon. The rain snow line will have changed very little since the overnight, despite cooler air moving in aloft, the boundary layer will warm due to diurnal effects, essentially leaving it in place. A couple inches of additional snowfall may occur before precipitation comes to an end across the Poconos and western Catskills. Even further west, under the vertically stacked mid-upper low and remnant parent low, scattered snow showers will dot the landscape with some lake enhancement perhaps bringing an inch or so. Temperatures will remain in the 30’s for most locations west of the Hudson Valley. East of the Hudson Valley temperatures across the higher terrain will also remain in the 30’s but elsewhere should see highs easily climb into the 40’s given the strong flow off the ocean. Winds will also be a concern as a 50kt flow at the top of the boundary layer and up to 80kts @850mb, pummel the highest peaks of Northern New York and New England. A still strong 20-30mph wind across the lower elevations of New England will make it feel very raw with the heavy rain falling.
Band of heavy precipitation continue to ever so slowly push northeastwards Tuesday night as the trough axis takes on an increasingly east-west tilt. 1040mb+ high pressure remains locked in place, just off the Labrador Coast and the strong 60-80kt low level jet centers in on Maine. With the occluded front pushing slowly off the coast, the 850mb 0°C isotherm may become a fixture across the extreme northwestern part of the state. There may be a very sharp cut-off line in this vicinity to who sees significant accumulations of snow or flooding rainfall now that the ground should be sufficiently frozen leading to most liquid precipitation immediately running off. QPF should range from an 1 to 2.5 inches across Maine during the overnight hours. Further south and west residual snow showers will be scattered about, perhaps mixing with rain along the coast. Temperatures will be in the 40’s along the Maine Coast with 20’s back towards western/central New York and Pennsylvania with 30’s in between.
Band of heavy precipitation remains focused on eastern Maine on Wednesday but will gradually weaken during the day as the best forcing begins to undercut the blocking ridge to the north, moving offshore. Elsewhere, under the upper trough axis, clouds and showers and rain and snow will continue. Temperatures will be near seasonal averages or slightly below, except for Downeast Maine where the onshore flow of milder Atlantic air will continue unabated.
Low pressure finally begins to pull north to James Bay by Thanksgiving. This will leave much of the Northeast with a decent day weatherwise. There will still be clouds around from moist cyclonic flow, with scattered snow showers around the lakes, but compared to what’s expected for the next 3 days Thanksgiving will be a walk in the park with temperatures close to seasonal averages.
With all the focus on the upcoming storm tonight through Wednesday the long-term portion of the forecast will be kept short and sweet. Another 500mb trough drops down out of Canada, rounding the base of the cut-off low pressure that will be affecting the Northeast over the next 60 hours, and rockets towards the East Coast by Friday afternoon/evening into Saturday. Rain and snow showers will be accompanied by this system, with the best snow chances across the interior with rain along the coastal plain. There's hints that this system will try and phase with a southern stream disturbance but this looks to occur too far offshore, sparing the region another significant precipitation event. Seasonably cold air follows in behind this system for the weekend along with minor lake effect snows. Potential exists for another potent disturbance to drop out of Canada early next week that will deepen and sharpen the broad trough over the United States east of the Rockies. This may translate into another significant storm with a wintry side across the Northeast to begin December with the arctic express open for business afterwards.
Radar: Northeast Region Loop
2008-09 Winter Forecast
Updated: 4:20 PM GMT on November 25, 2008
By: sullivanweather, 7:56 AM GMT on November 20, 2008
Current watches, warnings and advisories.
Forecast Discussion - Issued 11/20 @3:00am
Despite being without sleep for the last 24 hours I feel compelled to write tonight given the upcoming lake effect event expected to develop Friday and last into Saturday evening and, perhaps, Sunday morning. In the pipeline for Thanksgiving week is the potential for a major winter storm to affect the interior, but coastal locations may get in on the act too. More on that later but first thing first.
A weak clipper system is currently diving towards the Niagara Frontier at the time of this writing producing an area of light snow and flurries in the above-mentioned area and in a band extending east across south-central New York and north-central Pennsylvania. Outside of this area of light snowfall mid and high level clouds have helped to prevent another freefall in temperatures, as is occurring where the skies are mostly clear across much of central and western Maine and New Hampshire. Temperatures to begin the day will be in the teens across areas that remain clear, 20’s elsewhere.
As the clipper low continues southeastwards during the day on Thursday it will weaken markedly. The mid-level shortwave nearly loses its identity amongst the vorticity rope within the trough, the surface reflection of the low becomes absorbed within the pressure field of the larger low to the northeast over Labrador, a dry atmosphere and a weakening thermal gradient all spell a quick collapse to this clipper. However, lingering snow showers and flurries will still be present, mainly across the higher terrain of the Poconos and Catskills and extending back towards the Great Lakes. There will be a slight bit of lake enhancement that may deliver an inch or two to favored snow belt locations but accumulations elsewhere should range from a dusting to a very localized inch. Slightly milder airmass will be over the region with the –10°C isotherm @850mb retreating to central New York and New England but persistent clouds will play their role in keeping temperatures down across the southwestern two thirds of the region and should assert themselves once convective temperatures are reached across Maine. Along the coastal plain temperatures should have no trouble climbing into the 30’s (low 40’s urban centers). However, across the interior seeing temperatures exceed the freezing mark will be hard to come by, more so over northern New York and New England. Winds will be variable during the day, mainly from a southerly direction during the morning around 5mph, then shifting more westerly by afternoon as the clipper falls apart around 5-10mph.
Clouds, snow showers and flurries remain in place during the evening and into the overnight. Once again, most activity will be concentrated adjacent to the lakes thanks to their moisture/heat flux, though a veering flow ahead of an approaching arctic front will keep any snowbands on the move, limiting accumulations to a couple inches at most. Skies will be partly cloudy over the remainder of the region with a chilly light breeze. Lows will bottom out in the teens where skies manage to remain mostly clear. Elsewhere it’ll be in the 20’s once again, although along the immediate coast 30’s will do.
Friday will feature an arctic frontal passage that should deliver the coldest airmass of the season across the Northeast (yes, it’s gonna get even colder!) and set the stage for a widespread significant, in some cases substantial, lake effect event that’ll take us straight into Sunday. The arctic front will enter the Northeast after midnight and ooze over the region throughout the day on Friday. There’s no real sharp boundary with this arctic front and given the dry atmosphere in place any **snow squall activity looks to be isolated, but present none-the-less**. If one should encounter any of these squalls there will be rapid reductions in visibility and quickly accumulating snow. Behind the boundary lake effect snow will attempt to organize but will likely remain in broken line/cellular activity until later Friday afternoon as diurnal influences wane. With the passage of the arctic front temperatures are not likely to climb far from their morning lows and should begin to fall back down the ladder by mid-afternoon. A biting wind will increase out of the northwest at 10-15mph and be gusty at times.
**These are usually the most hazardous of all winter weather scenarios to encounter while driving, especially if it’s a locations first snowfall. Road will usually be salt-free and first flakes will tend to melt upon landing only to quickly refreeze as the heavier snow moves in, leaving a thin black ice coating. Also, the sudden shock of coming upon a squall may cause a loss of focus. I feel like hitting this hard because snow squalls are sort of the unmentionables of winter. Winter’s dirty laundry. There’s no specific advisory or warning for these events despite them being just as dangerous in terms of lives put at risk as a severe thunderstorm or flash flood. If conditions become bad enough, pull over and wait for the squall to clear; they usually do so in 10-15 minutes. After visibilities rise proceed slowly.**
The show is on Friday night as the coldest airmass of the season advects over comparatively blistering waters of Lake Erie and Ontario. DeltaT’s approach 25°C as the flow becomes increasingly aligned along a 305-310° heading. Inversion levels are nearly through the roof, over 10,000’ with tremendous lift intersecting through the snow dendrite growth region. Only limiting factor will be paltry synoptic moisture but given this airmass is straight down from the arctic, it’s not surprising. Georgian Bay connection will have to be watched and the implications downstream over Lake Ontario. The 305-310° flow is the tipping point in whether we see a multi-band event over central New York or a dominant band setting up. Sometimes what happens over Georgain Bay determines the dynamics of the band development over Lake Ontario. Regardless, the above mentioned favorable factors should lead to a 18-30 hour period of significant lake effect snowfall downwind of Lake Ontario and Lake Erie. By the time all is set and done accumulations of over a foot will be common across a good chunk of real estate downwind of both lakes. Should a more significant band develop at any time during this event even higher amounts may be realized in some of the more favored locations. Accumulating snow will extend pretty far from the lake as well, This event may require snowmap to be posted in an updated version of this blog tomorrow. Additional upslope snow showers will be found across the higher terrain of northern New York and New England in deep cyclonic flow. Skies should remain partly to mostly cloudy along the coastal plain, although a few snow showers or flurries might survive the trip over the mountains. Temperatures are expected to run 10-20 degrees below seasonal averages.
High pressure will be building in on Sunday but as seen earlier, the lake effect is sometimes hard to shut off, especially across central New York but the strong ~1035mb surface high building into the region will have a say in that. Across the remainder of the region it should remain partly to mostly sunny. There will be a slight recovery in temperatures too, although they will still run well below seasonal norms for mid/late November.
The next system of concern begins to move into the region Sunday night into Monday. Warm advection/isentropic lift precipitation may break out across northern New York and New England late Sunday night but most of the region will see just an increase in clouds. As the trough approaches during the day on Monday an expanding area of precipitation will enter western New York and Pennsylvania. Precipitation type is likely to be elevation dependent, with snow levels around 1,000’ south of the New York/Pennsylvania border. The trough continues marching east but slows its progression as it approaches the coast. Here’s where models continue to show disagreement. The Euro model insists that the 500mb trough will cut-off south of Long Island and back up over New York State while the Canadian and American models lift the trough out much quicker. Bottom line is that a significant synoptic snowfall is becoming increasingly likely across the interior. Thus far models have not had this storm becoming an inside runner and all take the system close to the 40-70 benchmark Tuesday. Deep vertically stacked low remains in the vicinity straight trough the Thanksgiving Holiday keeping the weather cold and unsettled. The big shopping weekend also looks to be in jeopardy as the longwave trough over the Northeast buckles once again as another potent northern stream disturbance is progged to drop down the backside of the trough as the relentless wintry weather pattern continues on.
Radar: Northeast Region Loop
2008-09 Winter Forecast
Updated: 1:24 PM GMT on November 23, 2008
By: sullivanweather, 3:43 PM GMT on November 18, 2008
Current watches, warnings and advisories.
Synopsis - Issued 11/18 @10:45am
A very January-like pattern for the Northeast this week as the northern branch of the jet dominates, sending weak impulses through the region in a brisk northwest flow. Accompanying these impulses will be an enhancement of snow showers followed by a reinforcing shot of cold air and a reorganization of the lake effect activity. Changes in the overall pattern begin to take shape by the weekend as Pacific energy manages to cut through the western ridge. Models are currently at odds on how to handle the new kid on the block but storminess moving across the country before the Thanksgiving holiday is becoming increasingly likely.
Short-term - Issued 11/18 @10:45am
The moisture-starved clipper low that had rocketed across the region over the last 12-18 hours is currently in the process of transferring its energy to a developing surface low several hundred miles off the Delmarva Coast. As this system passed by many locales along the coastal plain saw their first coating of snow this young winter season. Towards the north the lake effect machine was in full gear with several locations downwind of Lake Erie and Ontario receiving as much as a foot of snow or more. These lake snows have waned over the last 12 hours as the trough axis has passed by to the east and the flow has become anti-cyclonic and out of the north. Inversions are still high enough to allow for some weaker bands of snow showers to continue moving off the lake today, but these will be comparatively light compared to their weekend counterparts. Along the south shores of the lakes an additional 1-3 inches of new snow should accumulate today, with locally up to 5 inches in places that receive persistent banding. Even areas downwind of Lake Champlain should see several inches of snow given the favorable northerly wind trajectory. North winds may also provide the proper conditions for ocean-effect snow showers around Cape Cod. Snow to water ratios are rather high for such an early season event, in the vicinity of 15-20:1, making for increased ‘fluff factor’. Other scattered snow showers will dot the upslope regions of the higher terrain today, especially across New England where the trough axis will still be in the vicinity. Otherwise, with high pressure building in, locations away from the lakes and mountains should see a pleasant, but brisk day. Skies will be partly clouds with some passing cumulus clouds but these should tend to disperse after mid-afternoon. Cold air advection continues in earnest today, as the coldest airmass of the season moves overhead. 850mb temperatures will drop to –15°C to –10°C from north to south with 1000-500mb thicknesses down to 515dm across northern New York. Only areas along the southern coastal plain will see highs climb out of the 30’s today while interior locations struggle to the freezing mark. It would not be surprising to see highs only near 20°F in the higher peaks of the Adirondacks in the core of the coldest air. Winds will be out of the north at 5-15mph with higher gusts, especially along the immediate coast of New England, closer to the developing gale center offshore.
Northerly flow and cold air advection continue tonight as high pressure remains to the west, over the Ohio Valley. Scattered lake effect snow showers along the south shores of the lakes will continue, perhaps adding a couple inches to the rapidly building snowpack. Elsewhere will see partly cloudy to mostly clear skies and by far the coldest night of the season. Despite radiational cooling conditions being modest at best, many locations will still see their coldest night of the season. Lows will drop into the 20’s right down to the coast with teens across most interior locations. The colder sheltered valley locations amongst the higher terrain may even see single digits for lows tonight. Winds will slacken after sunset, but remain light out of the north.
The surface ridge axis moves across the Northeast on Wednesday providing a crystal clear start to the day, outside of any lingering lake activity, which should be confined to the immediate south shores. The airmass will modify only slightly, with 850mb temps rising a degree or two by late afternoon. However, this will reflect little at the surface due to a lowered mixing layer thanks to the high pressure overhead. Highs will climb into the 30’s across the interior with 40’s along the coastal plain from southern New England south to New Jersey. Once again the higher terrain will likely remain in the 20’s.
Mid/high clouds increase from the west late in the afternoon and early evening as the next clipper system approaches from the northern Great Lakes. Flow will begin to back towards the west and some lake effect activity may begin to stream off the east shores of the lakes in advance of any synoptic snowfall as the airmass is still sufficiently cold enough to support the lake effect process. Snow showers from the clipper system should spread into the region after midnight. One again, the clipper system is moisture starved and locations away from the snow belts shouldn’t see any significant accumulations, generally a coating or less. The cloud cover moving into western sections will put a cap on the temperature drop during the evening, but further northeast across New England and northern New York, ideal radiational cooling conditions will be met. Here temperatures should plummet after sunset into the teens and single digits, with 20’s expected along the immediate coast. Where clouds from the clipper system move in, lows will remain in the 20’s with lower 30’s along the Jersey Shore.
Mid-term - Issued 11/18 @10:45am
Thursday and Friday will be quite similar to the set-up yesterday and today as a clipper system moves off the coast, providing the impetus for the development of an offshore low pressure and the cold air advection in its wake for a period of significant lake effect snow. The airmass that follows in behind will be just a slight bit colder than the one currently over the region, with the 510dm 1000-500mb thickness contour moving as far south as the Mason-Dixon line and 850mb temps down to –17°C over northern New York State. Once again, the development of a norlun trough, which could provide a light snowfall to coastal locations, will have to be closely monitored. Lake effect in the wake of the clipper continues into Saturday before high pressure builds in and puts an end to the precipitation by Sunday. Temperatures throughout the period should average 5-15 degrees below normal.
Long-term - Issued 11/18 @1:45pm
Lots of uncertainty remains in the long term period that takes us right up to Thanksgiving. As mentioned above, models have yet to come to consensus regarding a chunk of Pacific energy that will ride over the western ridge and emerge on the lee side of the Rockies this weekend. The GFS model (and the latest GGEM) have suggested that this energy will coalesce into a potent clipper system in the Canadian Praries and dive southeastwards towards the Northeast, bringing a round of snow showers to the interior and rain showers along the coast. As the mid/upper trough axis approaches the coast a secondary low pressure may form to provide additional snows to the interior, especially Maine, Tuesday into Wednesday. Another wintry blast of cold air will follow with scattered lake effect/upslope snow showers in a northwesterly flow regime similar to the dominant pattern this week. On the other hand, the ECMWF model is showing a much less progressive system working its way from the Plains to the Great Lakes, and eventually the Northeast. Also slightly warmer, the ECMWF model would indicate the rain/snow line to be further north across the interior, initially. As the trough reaches the East Coast, a coastal low is progged to form that may provide a significant snowfall across the far interior and a rain to snow event for the coastal plain to go along with very windy conditions as the low wraps up over the Gulf of Maine on Thanksgiving Day. In addition, a very cold blast of arctic air follows in the solution provided by the ECMWF.
One thing the models do agree upon is the maintenance of a strong blocking ridge over the North Atlantic which should promote the continuation of troughiness in eastern North America for the foreseeable future.
Radar: Northeast Region Loop
2008-09 Winter Forecast
Updated: 6:40 PM GMT on November 18, 2008
By: sullivanweather, 11:16 AM GMT on November 14, 2008
Current watches, warnings and advisories.
Synopsis - Issued 11/14 @6:15am
A strong trough is currently diving into the Central Plains as an upper level low pressure spins along the north-central Gulf Coast. As this trough digs down to the lower Mississippi Valley it will phase up with the upper low over the Gulf, inducing cyclogenesis in the Tennessee Valley Friday evening. This low will move rapidly northeast to the eastern Great Lakes by Saturday afternoon and central Quebec by Sunday, sweeping a strong cold front, that will be accompanied with heavy rain, through the region. Much colder air, with a couple reinforcements, will follow straight through next week.
Near-term - Issued 11/14 @6:15am
Surface warm front currently extends from northern New York to Maine where it snakes just inland of the coast. North of this front temperatures are in the low 40’s while south of the front temperatures are in the upper 40’s to mid 50’s along with similar dewpoints. Very dense fog has formed in response, banked up against the Appalachians and extending down to the coastal plain. Pockets of drizzle and mist within this area of fog will make for a very treacherous ride into work this morning. Widely scattered showers linger across New England but these shouldn’t amount to much more than a tenth of an inch or less of precipitation through noon.
Short-term - Issued 11/14 @6:15am
A dry slot aloft will work over the Northeast this afternoon although significant low level moisture over the region will lead to another dreary day across much of upstate New York and interior New England. Weak lift provided by terrain/frontal boundary will keep drizzle and light showers ongoing through the day, especially over Maine. The frequent bouts of light precip will keep a cap on temperatures with highs likely remaining in the 40’s. Further south enough mixing may allow for the overcast skies to break some and there may even be a few peaks of sun. Being in the ‘warm sector’ (850mb temps 8-10°C) it may turn out to be a pleasant day once the morning fog burns off. Temperatures should have no trouble climbing into the 60’s along the coastal plain, across much of southern Pennsylvania and along the plains surrounding the lakes. Interior valley locations may challenge the 60°F mark but most of the higher terrain will remain in the mid to upper 50’s. Winds will be out of the south, veering to the southeast over New England around 5-10mph.
Fog develops once again this evening across much of the region, along with the ensuing mist and drizzle. Meanwhile, as a potent shortwave rounds the base of the aforementioned digging trough, cyclogenesis will occur just west of the southern Appalachians. Strong theta-e advection and coupled jet structure will promote a blossoming area of moderate to heavy rain to move into Pennsylvania and western New York during the late evening into the overnight. Rainfall amounts by morning should range from a third, to three quarters of an inch. The rest of the region will remain socked in with the fog and drizzle. Temperatures will remain nearly steady or drop only a few degrees.
Low pressure moves up the west side of the Appalachians on Saturday, reaching the St.Lawrence Valley by the evening. Strong southerly low level jet of 50-65kts develops out ahead of the low pressure, helping to transport deeper moisture across the eastern half of the region, along with some slightly unstable air. Precipitable water values rise to 2-3StD above climatology as Gulf and Atlantic are simultaneously tapped and 850mb temps reach their peak along the coast of 12-13°C. The oceans are much cooler this time of year and there will be an inversion to fight, but with such a strong flow just above the deck, the atmosphere will be sufficiently mixed for at least gale force winds to be felt along the coast and nearshore waters, not to mention the higher terrain from the Catskills and Adirondacks east into New England. There may be embedded elevated thunderstorms within the shield of precipitation across the region. SREF mean showing a couple hundred joules of CAPE from eastern Pennsylvania to southern New England combined with favorable jet dynamics in the exit region of a 140kt jet streak racing up the Mid-Atlantic Piedmont, sharpening baroclinic zone and increasing 850-700mb frontogenesis. In addition, as the strong cold front whips through the Northeast and breaks through the boundary layer inversion, a line of forced low-topped convection may develop along its flanks from eastern Pennsylvania across southeast New York into southern New England. Should this occur there could be some damaging winds. Dead braches on trees are usually taken down with these events with most of their leafy wind blocks gone and with the saturated ground, tree roots of weakened or diseased trees may not hold. Rainfall amounts of a half inch to an inch should be widespread with heavier amounts expected in convective showers. These heavy amounts of rain could fall in a short period of time leading to flashier creeks to have rapid rises in water level and promote ponding of water in low-lying areas. Temperatures ahead of the front will range from the 50’s to low 60’s. After the passage of the front temperatures will take a quick 10-15 degree drop and slowly fall thereafter back into the 30’s. Cold air advection behind the frontal boundary will also make for a gusty west-northwesterly wind of 20-30mph as any lingering rain showers change over to snow.
Mid-term - Issued 11/14 @6:15am
Cold front sweeps offshore the New England Coast by noon on Sunday. Moderate to heavy rain will fall out ahead of this front across much of the State of Maine Sunday morning with amounts ranging from a half inch to an inch and a quarter. Once again, the heavy amounts of rain in a short period of time could cause some minor flooding problems on flashier creeks and standing water in ditches and low-lying parking lots. Strong cold air advection continues behind the front with 850mb temps plummeting to –6 to –8°C by afternoon. The lakes will be active with bands of snow showers moving off on a 290-300° trajectory. A couple inches of snow may accumulate in areas that see persistent bands but there shouldn’t be anything significant until the passage of a clipper system on Monday. Wind vector turns more westerly Sunday night, lifting the bands north. This set-up usually favors areas just south of Buffalo and along the southern Tug Hill for heavier amounts, which could range from 2-6 inches overnight Sunday. Elsewhere will see partly to mostly cloudy skies with scattered snow showers across the higher terrain and surrounding the main lake effect bands. Temperatures will remain steady or only rise a couple degrees on Sunday across much of the region (upper 30’s/low 40’s interior, mid to upper 40’s coast) then fall slowly during the afternoon, although Maine will start the day rather mild (50’s) and will see sharp temperatures falls after the passage of the front.
A moisture starved clipper system will move through the region on Monday. Coastal regions will see nothing more than an increase in mid/high clouds but across the interior scattered snow showers will dot the region, enhanced by the lakes. Behind this clipper a reinforcing shot of cold air will be ushered into the region, with 850mb temps reaching their lowest levels of the season by Tuesday of –14 to –8°C from northwest to southeast. This will create extreme lake instability with deltaT’s rising over 20°C. Expect a decent multiband lake effect event, focused from northeast Ohio to extreme southeast New York off Lake Erie, including the Laurel Highlands and the Allegheny Front. In central New York, the I-81 corridor north of Binghamton to Syracuse and along the NYS Thruway to Utica stands to see the best chance at a significant snowfall from Lake Ontario. Vorticity rope in the 500mb trough may promote the development of an inverted trough that could even bring a light snowfall to coastal locales, but this will need to be further examined once the event comes within the range of the higher resolution models. For now, the main headlines will be the lake effect snow and the early winter-like temperatures.
Long-term - Issued 11/14 @6:15am
High pressure slowly builds towards the Northeast by Wednesday and Thursday, slowly cutting back on the lake effect in the snow belts and bringing fair weather elsewhere. Wednesday night should easily be the coldest night of the season for many locales. Model consensus breaks down by the end of the week as another potent shortwave dives into the trough carved out over the eastern half of the nation. This could turn out being just another clipper system and reinforcing shot of cold air, or something a little more substantial. Stay tuned.
The early start to winter shows no abatement heading into next weekend and beyond as strong north Atlantic blocking holds the eastern North American trough in place for the foreseeable future. Persistent lake effect, much below normal temperatures and the passage of several clipper systems will start to show its effects on the landscape with snowpack building and ice forming on smaller bodies of water. After a “White Halloween” will there be a “White Thanksgiving”? At this juncture, chances are looking good.
Radar: Northeast Region Loop
2008-09 Winter Forecast
Updated: 2:00 PM GMT on November 16, 2008
By: sullivanweather, 11:23 AM GMT on November 11, 2008
Lake-effect snow totals since Saturday
Spring Creek, PA - 11.0"
Stockton, NY - 10.0"
Mayville, NY 7.3"
Laurel Summit, PA - 7.3"
South Dayton, NY - 7.0"
Ridgway - 6.5"
Chautauqua, NY - 6.0"
Hooker, NY - 5.1"
Jamestown, NY - 3.0"
Current watches, warnings and advisories.
Synopsis - Issued 11/11 @6:25am
High pressure slowly builds over the Northeast over the next couple days bringing mainly fair skies and seasonably cool temperatures. Low pressure brings rain to the region on Thursday, perhaps beginning as a wintry mix across the interior, followed by a strong cold frontal passage this weekend in association with a digging trough east of the Rockies. Behind this front it will turn decidedly colder and lake effect activity will once again have to be dealt with. Deep trough over the eastern half of the country eventually draws down even colder air from the arctic mid to late next week that may very well stick around for the foreseeable future.
Short-term - Issued 11/11 @6:25am
The upper trough that has slowly progressed through the Northeast over the previous couple days will continue to make its presence felt over the region today, even though the trough axis currently lies from the Labrador Coast to New Brunswick. Cold westerly to northwesterly flow will continue to pour over the eastern Great Lakes today, providing occasional snow showers for areas downwind. DeltaT’s are running around 17-20°C, providing moderate instability, however, lowering inversions as surface high pressure builds in from the west, increasingly dry atmosphere and shear below the inversion will make for light accumulations. Mainly 3 inches or less can be expected today, concentrated along the southern Tug Hill plateau region downwind of Lake Ontario. Activity off Lake Erie has essentially ended. Along the immediate lake shores rain may mix with the snow during the peak heating hours. Additional snow showers will be found across the higher terrain of northern New England where favorable upslope flow and minor mid-level disturbances dropping through the trough will provide just enough forcing for these snow showers. Elsewhere across the interior, partly to mostly cloudy skies will reign, especially across New England and upstate New York. Clouds will be less numerous west of the Appalachians where high pressure will begin to assert itself. Along the coastal plain the stratocumulus deck will be much more broken as winds downslope off the mountains to provide drying in the lower levels of the atmosphere. Temperatures will be quite chilly today, as highs only struggle into the 30’s across much of the northern interior. The remainder of the interior and the New England coastal plain should see highs climb into the 40’s with low 50’s along the southern coastal plain. Winds will be out of the northwest around 10-20mph from upstate New York to New England with lighter winds towards the west.
High pressure continues to build into the Northeast tonight. At some point, the lake effect activity coming off Ontario will wane as inversions lower, although varying levels of cloudiness will still continue to move off the lake over adjacent onshore areas. Clouds and scattered snow showers will also continue to move through northern New England but this activity will also dwindle as the night progresses. With clearing skies and calming winds thanks to the high building in, radiational cooling conditions will slowly improve, especially after midnight. This effect will be most widely felt across the western half of the region. Lows will drop into the 20’s across most of the interior aside from localized readings in the teens in sheltered valleys and where snow cover remains from the recent lake effect. Along the coastal plain temperatures will fall into the 30’s tonight.
High pressure will remain in control on Wednesday. All lake effect/terrain enhanced snow shower activity will be over and skies will begin the day mostly sunny. Heights aloft will build and warm air advection will commence as 850mb temperatures rise several degrees during the day. Despite all the positives, high/mid level cloudiness will begin to encroach on the region in advance of the next system and the mixing layer will be very shallow, helping to keep temperatures from realizing their full potential. In fact, temperatures will only be a couple degrees warmer than today’s readings with highs in the 40’s across the interior once again with low to mid 50’s along the coastal plain. Higher terrain locations of northern New York and New England will remain in the 30’s.
Mid-term - Issued 11/11 @6:25am
Low pressure currently organizing over the Central Plains states will move along the broad southwesterly flow developing over the eastern half of the country and into the Northeast Wednesday night through Thursday night. Precipitation will break out from southwest to northeast, beginning around midnight across southern Pennsylvania and New Jersey and around daybreak along the New York-Pennsylvania border region. Thermal profiles suggest the leading edge of this precipitation may begin as a period of freezing rain and sleet as one heads north from northeast Pennsylvania, upstate New York and interior western New England. Here temperatures are expected to drop below freezing during the evening and slowly rise overnight as clouds thicken. However, when the precipitation starts temperatures will have yet to climb above freezing or will wet bulb back down to freezing for an hour or so before this colder surface air mixes out. Precipitation type issues won’t be a problem for the remainder of the region with temperatures solidly above freezing as precipitation begins. Amounts look to range from a half inch to an inch along the coastal plain with generally a third of an inch or less across the interior.
General cloudiness and light showers/drizzle will linger over the Northeast on Friday as a warm front attempts to lift through the region. As we head into the winter months it becomes harder and harder for such warm fronts to push through the Northeast and this time it should be no different. It’s very likely that the warm front will get hung up across upstate New York to northern New England somewhere, setting up a very sharp temperature gradient over the region. To the south of the front very mild air will once again flood into the region. Temperatures should easily climb into the mid to upper 50’s across interior locales and perhaps low 60’s reaching as far north as the New York City metro area. North of the front it will remain raw, with a stiff east wind and temperatures in the low to mid 40’s. Several model solutions also indicate a secondary weak wave of low pressure moving up along the coast that may provide a period of steadier rainfall. Finer details will be resolved in a later discussion.
Long-term - Issued 11/11 @6:25am
A strong cold frontal boundary will move through the Northeast Saturday and Sunday that will signal the beginning of a major pattern change across North America. A 50-60kt low-level jet will develop out ahead of this front, helping to transport copious amounts of moisture across the eastern half of the region and bring high winds to New England. With a good chunk of eastern New York and New England in the warm sector, a portion of these winds will be mixed down to the surface. Precipitable water values also rise to 150-200% of normal. Rainfall here should easily amount to an inch or more while locations further to the west, displaced from the deeper moisture, will get considerably less. Strong cold air advection behind the front will make for blustery west winds and a gradual increase in lake effect activity.
Looking ahead to next week, troughiness is expected to remain over the eastern half of the country. Wavelength and amplitude of this trough has varied greatly from run to run and model to model but general unsettled weather and below normal temperatures will continue. With this type of pattern, strength of shortwave disturbances dropping down the backside of the trough will ultimately determine sensible weather here in the Northeast but I would caution that chances for a significant snowfall will be above climatology given the cold air in place and the developing +PNA/-NAO pattern. Expect many of the area lakes across the interior to begin their annual freeze ups and locations downwind of the Great Lakes should come out of this with lasting snowcover.
Radar: Northeast Region Loop
2008-09 Winter Forecast
Updated: 11:41 AM GMT on November 11, 2008
By: sullivanweather, 11:41 AM GMT on November 04, 2008
A good phrase that may describe the upcoming winter season in comparison to last winter would be “Similar, but yet, so different.” La Nina is scheduled to make a return over the next couple of months. Atmospheric indicators have shown amplification of the residual La Nina-like pattern lingering since the spring but oceanic indicators at the surface had yet to materialize halfway through boreal autumn. This is starting to change. Beginning in late July, negative sub-surface anomalies appeared at thermo cline depth in the central Pacific and gradually spread eastward across the basin. Recently, these colder sub-surface waters have been upwelling to the surface, as shown in these most recent sea-surface temperature anomaly charts. Weather footnote, the system that brought an early arrival to winter here also brought an early arrival to winter all the way down to Mexico and may help to tilt the proverbial tipping point towards a full blown La Nina event. In a classic Tehuano wind event, a large region of cold upwelling has appeared in the Gulf of Tehuantepec. These events are normally followed by a surge in the trades across the east Pacific that may douse the remainder of the east Pacific of its surface warmth and allow the colder sub-surface waters to reach the surface completely. In addition, the upwelling portion of an oceanic Kelvin wave will propagate through the Pacific over the next month or so. This should trigger the long-awaited oceanic response into La Nina conditions by December.
So, what will make this winter similar to last?
Already apparent in the longwave pattern across the Western Hemisphere are developing positive height anomalies across the US southwest and most of the Atlantic basin, characteristic of a La Nina-like pattern. An extreme example of this last winter concluded with one of the driest ‘wet-seasons’ on record in California and every storm east of the Mississippi tracking from Missouri to Maine, leaving behind record breaking snowfall from the Great Lakes to New England and southern Canada as they rode around the periphery of a semi-permanent strong western Atlantic blocking ridge. This winter, the ridge-trough-ridge pattern won’t be as pronounced, but will still be present, leading to a majority of low pressure systems to follow a dominant storm path. However, as hinted at above, it’s been a struggle to completely return to a La Nina base-state. Since this’ll be a loosely established pattern heading into this winter, as opposed to last winter where La Nina was firmly established, there’s likely to be more variability to the weather pattern across the country this winter as strength and position of planetary ridges and troughs ebb and flow.
Also, like last winter, the oldest thickest sea-ice resides in the western hemisphere, with thin, recently formed, lower-concentration ice on the Siberian side of the Arctic. It comes as no surprise that the polar vortex early on in the season has formed over this region of thicker, high-concentration ice. This should ensure that winter will set-in across the northern-tier of the country on time this year and may do so with some bite. Longer range models have shown an immense arctic airmass developing over Alaska and western/central Canada later this month that will dive southwards into the US as boreal winter commences.
Answer, mean position of planetary ridges/troughs. Early-season availability of cold air.
However, as mentioned above, La Nina has yet to become a firmly established pattern and there are other factors that play critical roles in winter variability here in the Northeast. Those are the indices that measure the proceedings of the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO). These indices correspond to the weather patterns over the arctic/sub-arctic and the North Atlantic Ocean, including Western Europe and those of us here along the east coast of North America. Unlike last winter, the NAO, which spent most of the season in positive phase, will tend to be in negative phase this winter. In doing so, there’ll be more, longer periods of Greenland blocking and ensuing downstream/upstream troughiness. This will promote a greater number of storms that undergo coastal redevelopment, holding colder air locked into the Northeast. Last year a majority of these systems remained progressive, moving through the Great Lakes to New England with little coastal redevelopment. Ultimately, timing decides everything, but with more time spent this winter under conditions favorable for coastal redevelopment and the southeastward shift in storm track due to a more negative NAO, seasonal totals along the coastal plain and northern Mid-Atlantic should be greatly increased compared to last winter. Correspondingly, this will leave northern New England south of the belts of heavy snowfall this winter, although enough variability and active storm track will bring them average to slightly above average snowfall. The likely winners in the snowfall department this winter will be from north-central Pennsylvania to interior central New England. Active, southeastward shifted storm track combined with being in deeper cold air for much of the season will lead to some large seasonal snowfall totals. This area saw many storms begin with snow, then change over to sleet, freezing rain and eventually rain as warm air surged north with every storm that moved west of the area last winter. This will be less of an occurrence this winter as warm air will fail in many attempts at spoiling the snow. Recent patterns in the AO has been for wild swings from extremely positive to extremely negative, typically taking 6-8 weeks to complete this cycle, then flattening out over the ensuing 6-10 weeks before undergoing another gyration. This had recently repeated itself twice extending back to last spring and appears to be in the midst of beginning another. Much of the month of October has been spent in positive AO but recent models show a dive into the negative starting the second week of November that may carry through to the end of the month. Following this pattern the next sharp gyration of the AO will be in late January to mid February. There’s likely to be a large East Coast snowstorm during this period.
Adding variability to the pattern will be a more pronounced negative PDO pattern across the Pacific. The large pool of below normal SST’s across the northeast Pacific, off the West Coast, and general troughiness centered over the Gulf of Alaska, a constant supply of Pacific moisture and energy will be introduced into the North American pattern. Above average storminess from northern California to southern British Columbia will lead to another season of impressive seasonal rain/snow totals while areas of southern California will continue to endure severe drought. Much of this energy will continue on through the central/northern Rockies and into the Plains with a below average number of systems becoming trapped in the Southwest. East of the Rockies, low pressure systems will tend to follow a tight baroclinic zone around the periphery of the western Atlantic high pressure. This is the pattern similar to last year. But unlike last year, the La Nina pattern in the atmosphere isn’t as strong. So there’s likely to be less of a representation of the western Atlantic ridge and greater variability in the storm track as the La Nina pattern tries to get a hold on things. Also, the NAO is forecast to spend more time in negative territory, which should flatten the top, erode, or eliminate in some cases, the western Atlantic ridge. This will account for a greater number of storms to move southeast of the dominant storm track seen last winter. This will result in less snowfall than last year’s record amounts within a couple hundred miles of the US-Canadian border region and more snowfall over the Ohio Valley, southern half of the Northeast and northern Mid-Atlantic. I would also be concerned about a major ice storm across the Carolinas and northern Georgia this winter, given the availability of arctic air this winter and a southward shifted storm track. Again, the next expected fluctuation in the AO towards the end of January sticks out as the most probable time for such an event. Freezing precipitation problems should also extend into the region outlined for greatest risk at exceeding seasonal snowfall averages. As seen last winter, there’ll be many warm advective/isentropic lift precipitation events. This is always a classic set up for warm air aloft to spoil many-a-snowstorms by changing precipitation to sleet and freezing rain.
There’s lots going on here but I’ll try to make it understandable.
Blue “H’s” are mean positions of high pressure
Red “L’s” are main development areas of low pressure systems
Red curved lines extending away from “L’s” are the dominant storm tracks, thickness of line indicates frequency; thicker=more frequent.
Black line is the mean position of the jet stream
Blue circles indicate colder than normal temperatures
Red circles indicate warmer than normal temperatures
Green circles indicate greater than average precipitation
Yellow circles indicate less than average precipitation.
The highest range of variability in storm track will be over the Pacific Northwest Coast and across the eastern half of the country centered from the mid-Mississippi Valley and the Mid-Atlantic. Broad troughiness will extend across a good portion of the country, allowing for cold Canadian air to bleed southward into the northern-tier states. Strength of coastal and near-shore ridges will determine the extent of the cold air throughout the season but the north-central states should find themselves centered under this airmass for a good portion of the winter as cold zonal flow will tend to dominate the winter pattern. Position of western Atlantic ridging will allow for the Gulf of Mexico to be tapped, as opposed to capped, as storms develop across the center of the nation. This will allow for wetter than average conditions extending from Missouri to the Northeast, similar to last year but southeast shifted a hundred miles or so given the expected southeastward shift in storm track. Dry conditions are to be expected again across the northern High Plains, the Southwest, and the Southeast.
Here in the Northeast an active winter season is expected. As mentioned above, we’ll be close to the main storm track for much of the winter season. The expected development of La Nina will keep a mainly positive PNA pattern going for much of the winter. A change from last winter will be the strongly negative PDO, and (perhaps) a weakly negative NAO. These will conspire to keep coastal ridging in check, allowing for more Pacific energy to enter the western states and allow more energy to move off the East Coast, as opposed to moving into Canada as seen last winter.
With the baroclinic zone shifted closer to the coast this winter season, a greater number of storms will redevelop upon cross the Appalachians along the coast, helping to hold cold air in across the Northeastern states. This will lead to greater than normal precipitation and snowfall across a good portion of the region. Near average snowfall can be expected across the northern third of the Northeast as this region will miss more storms to the south this season. This region will also see below average precipitation but with high snowfall ratios expected being deeper in the colder air normal seasonal snowfall totals should be achieved.
Cold air will also find its way into the Northeast with greater frequency this winter given the southward shift in the jet stream expected. At least the northern half of the region should see below normal temperatures this winter with near normal temperatures across the southern half of the region where equal bouts of cold and warm air is expected being in close proximity to the storm track.
Current watches, warnings and advisories.
Forecast discussion - updated 11/06 @6:30am
Strong blocking southeast of Greenland has been making its presence felt across the North Atlantic and eastern North America. Initially, with a supply of cold air in place, this blocking helped to spawn our early season snowstorm last week. As these ridges have failed to break down recently, forcing the jet stream to drive around their northern periphery, that supply of cold air has been exhausted and the airmass across the mid-latitude belt of almost the entire planet has been much warmer than average this previous week. Also, with the jet stream displaced to the north, it’s been slow going in the mid-latitudes. GOES satellite imagery depicts three stacked cyclones between 100°W and 50°W, left behind by the jet stream. One over the Central Plains, another off the Delmarva Coast, and a third about 1,000 miles east of Bermuda. To add in another flavor to the mix, Tropical Storm Paloma has recently formed in the southwest Caribbean Sea. This may end up being the wild card system that will force a pattern change as it moves into the mid-latitudes next week.
Here in the Northeast we’re dealing with system #2, the Delmarva low, which has spun back a band of rain across much of the coastal plain and adjacent inland areas from southern New England to eastern Pennsylvania. Clouds from this storm extend over much of the region, with only extreme northern Maine and areas west of the Appalachians escaping them. Other than scattered showers, that may fall hard for a time this morning out over southeast Massachusetts, this system will be nothing more than a nuisance for non-coastal locations. Along the coast is where the storm will pack a bit more punch. The wind and water facets of this storm will be the main focus as a persistent long fetch of southeasterly winds have piled water along the coast and kicked up some high surf. Minor coastal flooding and beach erosion at times of the next few high tide cycles until Friday afternoon will be the result. The clouds and precipitation associated with this system will slowly begin to clear out of the region on Friday and Friday night but cloudiness will spread over western sections in advance of the Plains storm. Temperatures will average 5-10 degrees above normal over the short-term period to close out this week.
System #3 over the Central Plains will slowly work its way eastwards, reaching the Northeast by Saturday. The cyclone itself will be well to the northwest over Canada, but it will sweep a cold front through the region that will be accompanied by a band of rain. Axis of heaviest rainfall looks to set up across upstate New York where a half inch to an inch of rainfall may occur. Elsewhere, rainfall should amount to a half inch or less. The front will clear the coast on Sunday and behind it temperatures return to near normal levels for early November. 850mb temps fall to –3°C to –6°C and given sufficient synoptic moisture in place, lake effect rain and snow showers downwind of the lakes will occur. This continues into Monday as the axis of the trough pulls through and a secondary shot of cold air moves in. The combination of continued cold air advection and general cloudiness in place should conspire to send temperatures back to slightly below normal levels.
High pressure ends the lake effect precipitation by Monday night or Tuesday, though it will remain chilly. 850mb temps will remain below 0°C north to south and high clouds will already be spilling into the region ahead of a shearing system over the Mid-Mississippi Valley/Tennessee Valley region. Eventually, some precipitation from this system will sneak into Pennsylvania and New Jersey during the late evening on Tuesday but it will be working against a very dry airmass in place. Model consistency breaks down beyond Tuesday, and given the plethora of regional pattern changes across the northern hemisphere expected as the anomalous mid-latitude ridging breaks down confidence in any one forecast is rather low. First big challenge for the models as we inch closer to boreal winter. It’ll be interesting to see if the ECMWF reasserts itself as the dominant performer during these months, or if the recent success of the GFS model continues. Going with the GFS, the system over the Tennessee Valley slowly works its way to the Mid-Atlantic and up along the coast. It’ll be rain for most but upstate New York and northern New England may see a few wet flakes. Needed to be watched is Paloma and any possible interaction between the two systems.
As this storm finally gets a move on a strong Pacific jet will be slamming ashore the West Coast. This is likely to coalesce into a significant trough on the leeside of the Rockies as the new progressive meridional pattern brings storminess to the nation next weekend into the following week.
Radar: Northeast Region Loop
Updated: 11:42 AM GMT on November 06, 2008
By: sullivanweather, 5:36 AM GMT on November 03, 2008
Current watches, warnings and advisories.
Synopsis - Issued - 11/03 @12:30am
A rather busy week of weather ahead, despite the strong ridging that will be nearby for much of the next 4-5 days. A hybrid system off the East Coast will make an uncomfortably close approach to the region by Wednesday night, moving to the Canadian Maritimes by Friday evening. The next trough moves through the Northeast this weekend with a return to normal temperatures after its passage to begin next week.
Short-term - Issued - 11/03 @12:30am
Strong ridge that has moved over the region, bringing fair skies and a rather crisp early November airmass, will build offshore this week becoming a key player in the sensible weather, especially for coastal residents; more on that later. Today, a weak shortwave, associated with a band of showers over Michigan at the time of this writing, will attempt to move into the Northeast. Aforementioned ridge centered offshore will effectively shear this system apart, leaving only a few light showers dotted over western/central Pennsylvania and New York. Otherwise, there’ll just be an increase in cloudiness today. This won’t allow the full potential of warming airmass aloft to be realized but temperatures will still be about 5-8 degrees warmer than Sunday. Highs will range from the 40’s over the northern third of the region with 50’s elsewhere across the interior. There’ll even be a couple pockets of 60’s across the southern coastal plain and western Pennsylvania. Partly to mostly cloudy skies continue into the overnight. Temperatures won’t fall far from their daily highs in response. Lows will range from the mid to upper 30’s across the northern interior to the low to mid 40’s across the remainder of the interior. Along the coastal plain it will be rather mild, with lows in the upper 40’s to mid 50’s in the urban centers.
Varying levels of clouds continue to be about the region on Tuesday, as a remnant of the mid/upper disturbance remains overhead. Light onshore flow may advect a shallow marine layer along immediate coastal locations as well. Despite the clouds, enough sun will shine through this thinner layer of mid/high clouds, and combined with the mild airmass entrenched over the region, for a most comfortable autumn day. Temperatures will take a few more upwards ticks, with 40’s confined to the highest terrain. Elsewhere 50’s will be common and the 60’s will expand to cover much of the coastal plain, southern interior, lake plains and interior valleys. Weak onshore flow will further push marine layer inland during the overnight hours Tuesday. Across the far interior skies will begin to finally clear out as ridging builds in the mid/upper levels. Lows will be, on average, 5-15 degrees above average.
Mid-term - Issued - 11/03 @12:30am
Offshore high pressure, whose ridge axis extends back towards the eastern Great Lakes, will be the dominant weather feature by midweek, bringing fair skies and mild temperatures. Attention will focus on an oceanic storm, likely a hybrid system, developing off the Southeast Coast, between Bermuda and The Bahamas. Blocking ridge in place south of Nova Scotia will bring this low pressure close enough to the coast for some effects to be felt. Uncertainty exists to the extent in which coastal and adjacent inland areas will be affected, if at all, but this is a developing situation that will require closer examination in ensuing model suites. In any event, the gradient will tighten over the southern half of the region bringing stiff onshore east-southeasterly winds. Long fetch will build the surf along the coast and may eventually lead to coastal flooding and beach erosion concerns. Meanwhile, towards the interior with the ridge axis overhead mainly fair skies and mild temperatures will dominate. Here, temperatures will continue to average 5-10 degrees above normal.
Long-term - Issued - 11/03 @12:30am
Next trough approaches by the weekend but with low pressure riding up into the Great Lakes, well west of the region, we’ll be on the warm side of the storm. Early call on rainfall with the cold frontal passage is around a half inch to an inch, but this may be focused on the eastern half of the region. Colder air arrives by Sunday and should get the lakes cranking once again, although this looks to be a minor event at this juncture.
Radar: Northeast Region Loop
Updated: 5:49 AM GMT on November 03, 2008