Northeast Weather Blog

Strong cold frontal passage today

By: sullivanweather, 6:28 AM GMT on September 28, 2009

Current watches, warnings and advisories.


Eastern US current watches/warnings
Fig.1 - Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.

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Forecast Discussion


Synopsis - Issued - 9/28 @2:30am


A rather deep early-season trough will be positioned across the Great Lakes region on Monday as a strong shortwave disturbance rotates down the backside of the trough through the Ohio Valley and eventually into the Northeast. This disturbance will help spark a line of showers and thunderstorms along and ahead of a sharp cold front moving across the Northeast. Following the cold front will be a very autumn-like pattern for the upcoming week. A high latitude blocking pattern over the North Atlantic will keep the deep trough in place over the Northeast leading to cool and unsettled weather through Friday for most, if not all, of the region. The trough finally begins to lift by the weekend but only as another cut-off low slowly rotates towards the region from the Midwest. Being a bit further south than its predecessor, this second cut-off low won’t be able to tap into much cold air from the north and temperatures will be a bit milder as it moves overhead during the beginning of next week.



Short-term - Issued - 9/28 @2:30am



The low pressure complex which provided a soaking rainfall for much for much of the Northeast over the weekend will pull into the Canadian Maritimes on Monday, with lingering showers over northern Maine ending by noon. Meanwhile, to the west, a strong cold front will enter western New York and Pennsylvania by daybreak. Strong to severe thunderstorms is currently being produced from this cold front over Michigan and Illinois and these lines of storms may hold together during the overnight and push into the western portions of the region by daybreak. Between these two areas of precipitation skies will be partly to mostly cloudy. Areas of low clouds, fog, mist and drizzle will be scattered about the region, mainly across interior valleys. Temperatures will begin the day in the 50’s across the interior and northern New England coastal regions, with low 60’s along the coastal plain from New Jersey north to southern New England.
A rather active day of weather across the western half of the region on Monday as the aforementioned strong frontal boundary continues to push east. This front is connected to an area of low pressure over the Great Lakes that will be intensifying as the day progresses, tapping into the energy provided by the potent shortwave diving down into the trough. As the area of low pressure strengthens and pushes towards the Northeast winds aloft will increase in response, with a 40-50kt low-level jet developing across the western portions of the region during the morning hours. In addition to the lift provided by the surface front, the region will also lie in the dynamically favorable left-exit region of a 70-80kt mid-level jet (best dynamics will be over the Niagara Frontier). A convective line of showers along the ahead of the cold front pushing across the region will have the capability of producing marginally severe wind gusts as it taps into those stronger winds 5-7,000’ above the surface. Behind the front it will get quite blustery in the cold advective pattern and rather strong winds aloft (30-40kts). Temperatures will slowly drop from mid-morning on under the stratocumulus deck. Further east, from eastern New York/Pennsylvania into western New England, there will be breaks of sun during the morning hours before the frontal passage, allowing for modest surface heating. Winds will increase as well with mixing to 875mb in a strengthening southwesterly flow of air aloft. This will help to advect a bit milder airmass into the region with 850mb temps rising to 11-14°C by afternoon, slightly cooler from the Adirondacks on north, allowing surface temps to easily climb into the 70’s, with a few low 80’s possible across the urban corridor (60’s Adirondacks on north). Moisture will also be pooling out ahead of the front (precipitable water contents rising to 1-1.3”) yielding several hundred joules of CAPE. Despite the better low-level thermodynamic set-up across this region the front will begin to outrun the more important (in this case) jet dynamics, low-level jet streak, and will also encounter warming temperatures aloft (a slightly capped atmosphere). Hence coverage of precipitation associated with the front will begin to wane, especially east of the Hudson Valley. Across the far eastern and northern portions of New England, the day will actually improve as it progresses. Low pressure will be slowly moving away, being replaced by southwesterly flow developing ahead of the low pressure over the Great Lakes. Cloudy skies to start will gradually give way to some break of sunshine. Highs will climb into the 60’s.

The cold front continues its march across New England Monday night. Showers will continue along and out ahead of it, with the greatest concentration of precipitation across Maine, closest to the better jet dynamics, but rainfall should average under half an inch. Meanwhile, low pressure will become stacked over southern Ontario with wrap-around moisture and some lake enhancement producing showers in/around the Great Lakes. Between these two areas of precipitation skies will be mostly cloudy with blustery winds in the cold advection behind the front. Temperatures will drop into the 40’s across the interior with low to mid 50’s along the coastal plain.

Deep, stacked low pressure over southern Canada will continue to plague the Northeast during the day on Tuesday. Cooling air aloft and deep cyclonic flow over the region will yield a rather cloudy day over the interior as wrap-around moisture, lake-enhancement and orographic lift combine to produce widely scattered showers (a bit more numerous closer to the lakes/terrain of northern New York/New England). Along the coastal plain some downsloping will cause breaks in the cloud cover, but it will still feel noticeably autumn-like in comparison to Monday. Temperatures won’t climb far from their morning readings as 50’s are expected across the interior with low 60’s along the coastal plain. A few locations across the higher terrain of northern New York and New England may even fail to get out of the 40’s!



Mid-term - Issued - 9/28 @2:30am



Deep upper trough lingers over the Northeast through Wednesday and Thursday. During this timeframe a couple additional shortwaves diving down the backside of the trough will introduce a reinforcement of colder air from Canada. The Great Lakes will become active as greater delta T’s develop in response to the cooling airmass. Additionally, there will be renewed chances for vorticity advection showers across the remainder of the region. Depending on model of choice, 850mb temperatures are forecast to dip down to the -2 to -6°C range as the core of the cold airmass moves in. This may be cool enough for snow to mix in at higher elevations during the overnight hours. Temperatures will average 10-15 degrees below normal, with the greatest disparities apparent in the daily max’s.



Long-term - Issued - 9/28 @2:30am



The deep trough will slowly lift out of the region Friday and Saturday, allowing for temperatures to warm. However, precipitation chances will continues as the next area of low pressure slowly pushes east from the Midwest. Warm advective/isentropic lift showers are expected to develop across New York and Pennsylvania during the day on Friday and lift north into New England on Saturday in an area of warm frontogenesis at the nose of a developing 30-40kt low-level jet. By Sunday the low over the Midwest will lift into the Great Lakes in response to a significant trough moving into the Western US. As low pressure lifts into the Great Lakes another frontal passage will occur for the Northeast Sunday into Monday.

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Radar: Northeast Region Loop

NE radar
Fig.2 - Radar loop of the Northeast region. Courtesy of Weather Underground.


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Local SST's

Northeast SST's
Fig.3 Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.


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Autumn has arrived

By: sullivanweather, 5:44 AM GMT on September 12, 2009


Current watches, warnings and advisories.


Eastern US current watches/warnings
Fig.3 - Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.

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Forecast Discussion


Synopsis - Issued - 9/12 @1:40am


Stacked low pressure over New Jersey will gradually fill and lift out of the region by the end of the weekend, leaving clearing skies in its wake. Fair skies and warm temperatures will persist into Monday but a backdoor front will drop through the Northeast Monday night and Tuesday. For most locales this will be a dry frontal passage but the airmass behind the front is rather chilly. Both Tuesday and Wednesday nights could feature widespread frost/freeze conditions across the North Country under the surface high, possibly ending the growing season. This high moves offshore on Thursday with return flow pumping milder air back into the Northeast to end the week.



Near-term - Issued - 9/12 @1:40am



A stubborn area of low pressure, currently over southern New Jersey, has played havoc with the weather along the Northeast Coast from Cape Cod on south since Tuesday. Valiant high pressure over New England, which led to fantastic weather there, eventually lost the battle and has exited, stage right. Since departing, moisture has spread up the coast in the onshore flow ahead of the low, backing showers northwestward across the southern half of the region. Most of the heavy rain associated with the low has now ended, though one pocket of heavier showers is currently moving into the Poconos and Lehigh Valley of Pennsylvania this overnight. This region may see up to a half inch of rain overnight from this area of heavier showers. Elsewhere, a broken line of showers extends from Buzzards Bay to the Albany, NY area to the Finger Lakes region with a smaller pocket of light showers falling in central Vermont and New Hampshire. Across these areas rainfall amounts should range from a few hundredths of an inch to a quarter inch in more persistent bands. With the ample amounts of low-level moisture given the onshore flow, fog, mist and drizzle has been prevalent across most locales. Further north, over Maine, a narrow ridge axis remains and skies have been mostly clear throughout the night. Temperatures here, where skies are clear, should range from the mid to upper 40’s. Areas socked in under the clouds will see temperatures mainly in the 50’s with 60’s confined to the coastal plain and under the stacked low where dewpoints are higher.



Short-term - Issued - 9/12 @1:40am



The low pressure will slowly fill and move eastward during the day on Saturday. Onshore flow will still keep clouds and showers across a good portion of the region, though areas across western Pennsylvania will see some improvement to the weather by the afternoon hours as high pressure builds in from the west. Northern Maine will also escape the foul weather as the narrow ridge axis will still be in place, keeping the coastal low at bay. The sunny skies across Maine will allow temperatures to climb into the 70’s. The same holds true for areas across western Pennsylvania where clouds will be present, but enough breaks of sun will manage to push temperatures out of the 60’s. Closer to the area of low pressure, folks won’t be as fortunate. Temperatures won’t climb far from their morning readings and many locales across the Poconos, Catskills and Berkshires will remain stuck in the upper 50’s. Highs elsewhere will be in the 60’s. A raw east to east-northeast wind will continue to blow at 10-15mph across the interior with 20-25mph winds along the coast.

The low starts to pull east at a faster clip Saturday night as a northern stream trough approaches. Plenty of low-level moisture will remain trapped across the Northeast leading to another damp and dreary night with widespread low clouds, fog and drizzle. Clouds will even increase across Maine; not from the coastal low but rather a northern stream trough diving south from Canada. Temperatures will range from the 50’s across the interior with 60’s along the coastal plain.



Mid-term - Issued - 9/12 @1:40am



Low pressure will be moving out to sea early on Sunday as the northern stream trough moving the coastal along sweeps off the coast with weak cold air advection following in behind it. Skies will be mostly sunny across the western half of the region but cyclonic flow combining with weak spokes of energy rounding the trough over the Canadian Maritimes will keep clouds and scattered upslope showers prevalent across northern New England, possibly extending back towards the Adirondacks. Highs will be quite mild where the sun is ample, with temperatures easily climbing into the 70’s across the interior with some low 80’s along the coastal plain given the downslope flow and mixing to 850mb, where temps are in the 12-14°C range. Loss of insolation will end the threat of showers across New England, with skies gradually clearing after midnight as drier air filters in. Elsewhere across the region skies will be mostly clear for the entire overnight period, with lows mainly in the 40’s and 50’s across the interior with some 60’s along the coastal plain.

The Northeast will find itself nestled in between systems on Monday leading to a fine day for most, the State of Maine aside. There will be varying levels of mid/high level cloudiness ahead of a shortwave diving south from Quebec, with most coverage across the northern tier of the region. In fact, clouds may get quite thick over northern Vermont, New Hampshire and Maine by the afternoon, helping to keep a lid on temperatures here. To the south, further from the influence of the approaching shortwave, skies will feature more sunshine and temperatures will get quite warm in response. Highs will once again reach into the 70’s to low 80’s, slightly above the norm. However, northern locales will see highs held in check by the clouds with highs reaching into the 60’s before leveling off after the noon hour. The shortwave will make quick progress south, reaching the US-Canadian border by daybreak on Tuesday. There’s not much moisture associated with this system but the strong burst of PVA from the mid-level impulse and strong forcing along the surface frontal boundary should kick off a line of convective showers across Maine during the overnight hours. This line of showers will extend back towards the southwest to the Adirondacks but coverage will be more isolated away from the better dynamics associated with the mid-level disturbance. Further to the south, from the Niagara Frontier to the central New England coast, clouds will increase during the overnight while areas even further south should see a mainly clear night. Temperatures will range from the 40’s across the North Country to the 50’s across the remainder of the interior with 60’s along the coastal plain.



Long-term - Issued - 9/12 @1:40am



The long term period begins with the cold front crossing the region on Tuesday. The front will come through dry and merely increase the coverage of mid/high level cloudiness. Following in behind the front will be the coldest air of this young meteorological autumn. Highs will remain only in the 50’s behind the front across northern New York and New England with 60’s and 70’s further south. As high pressure builds in Tuesday night and skies clear expect a fast drop in temperatures during the evening. Winds will die down after midnight allowing temperatures to drop even further, into the 30’s across the North Country, allowing for areas of frost to develop. Further south frost isn’t expected, aside from the terrain of northwest Pennsylvania, but it will still be quite chilly. Lows will bottom out in the 40’s away from the coast with only low to mid 50’s along the immediate coast and urban centers.

High pressure remains anchored over the Northeast on Wednesday providing a spectacular day, weatherwise. Highs will only top out in the 50’s and 60’s with the chilly Canadian airmass in place but skies will be filled with brilliant sunshine and winds will be light. These clear and calm conditions will persist into Wednesday night allowing for ideal radiational cooling conditions once again for much of the region. Only the southern and western portions of Pennsylvania will see an increase in high clouds during the night, helping to prop up temperatures in this region, mainly in the 40’s. Further north and east, under the core of the cold airmass, temperatures once again will drop low enough to produce frost and freezing conditions. The North Country of northern New York and New England will be the prime locales once again, but areas extending down into the Berkshires and Catskills may also see temperatures drop down into the mid 30’s, cold enough for scattered frost. Closer to the coast lows will moderate into the 40’s and low 50’s.

The strong surface high will yield one more day of good weather on Thursday. Fair skies will be seen at most locations, although mid/high level clouds will be increasing from the southwest, mainly across New York/Pennsylvania, as an area of low pressure slowly moves northeast from the Gulf States. Precipitation from this low will reach the Northeast by Thursday night into Friday as high pressure moves offshore. The return flow around the backside of the high will allow temperatures to climb back to seasonable levels for mid-September on Friday but a northern stream trough quickly scooping up the southern stream low will send a cold front through the region Friday night and Saturday. The 0°C 850mb isotherm once again penetrates into New England behind this front. Autumn is certainly here!


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Radar: Northeast Region Loop

NE radar
Fig.4 - Radar loop of the Northeast region. Courtesy of Weather Underground.


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Local SST's

Northeast SST's
Fig.5 Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.


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About sullivanweather

Thomas is an avid weather enthusiast, landscaper and organic gardener. This blog is dedicated to Northeast and tropical weather forecasting. Enjoy!

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