Thomas is an avid weather enthusiast, landscaper and organic gardener. This blog is dedicated to Northeast and tropical weather forecasting. Enjoy!
By: sullivanweather, 8:58 PM GMT on January 15, 2010
A moisture-laden southern stream low pressure will move towards the Northeast late this weekend spreading rain, ice and snow across the region, possibly in significant amounts across the interior.
Current watches, warnings and advisories.
Fig.1 - Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.
Synopsis - Issued - 1/15/10 @ 4:00pm
Split flow regime will dominate the US for the upcoming week with the bulk of the activity occurring in the southern branch. One system originating from the southern stream will move into the region late this weekend and perhaps another late next week. The January thaw continues for at least one more day in the near term before a storm system working northeastward out of the Gulf of Mexico spreads precipitation back across the Northeast by Sunday and Monday, possibly as heavy wet snow across the interior. Following the passage of the storm a weak upper trough settles south for Tuesday and Wednesday bringing a return to seasonable temps along with a few snow showers across the interior as the next system of importance gathers strength over the South, possibly reaching the Northeast by Thursday.
Short-term - Issued - 1/15/10 @ 4:00pm
A mild afternoon is shaping up for most locales across the Northeast this Friday as temperatures run 5 to 10 degrees above normal for the first time in nearly 3 weeks (after Christmas storm). Along the coastal plain temperatures have climbed into the mid to upper 40’s under a moderately thick mid/high level cloud layer, which has allowed feeble insolation through the cloud canopy. However, further inland a weak cold front is sagging southward with much thicker low-level clouds in its wake. Despite the thick cloud cover and being behind the front temperatures are still residually mild with many locales well into the 30’s. The colder temperatures this afternoon are found far to the north, over northern New England, where temperatures are hovering within a few degrees of freezing. But for mid-January that’s about 10 degrees above normal as well. However, these near-freezing temperatures have been an issue as some spotty light drizzle has sprung up in various locations behind the frontal boundary. The main problem area for this freezing precip has been across northern Maine but some light freezing drizzle may come to fruition in areas across upstate New York and central New England later this afternoon and this evening where all-liquid drizzle now may changeover as temperatures slowly cool as we lose diurnal influences.
The cold front loses definition tonight as it becomes aligned to the flow aloft. Clouds will be present for a majority of the overnight but will start to slowly break-up as we approach daybreak and drier air filters in from the west. Temperatures will only slowly fall from their readings today due to the cloud cover. Expect lows in the 20’s across the interior (a few teens across the higher terrain) with 30’s down along the coastal plain.
Weak high pressure building south of the region will allow for a more pronounced westerly flow on Saturday as skies slowly clear across the southern half of the region. To the north a strong cold front will be moving in the northern branch of the jet, grazing by northern New York and New England. Numerous snow showers and a few squalls can be seen with the passage of this front with much colder air blasting in behind it. This will yield a rather pronounced temperature gradient across the region tomorrow as the southern half of the region should see no trouble climbing into the 40’s under decreasing clouds and mild 850mb temps. Across northern New York and New England the frontal passage should keep temperatures holding steady or see them slowly fall throughout the course of tomorrow, starting in the mid 20’s to low 30’s in the morning – falling into the upper teens to mid 20’s by late afternoon. Between these two regions, along I-90 give-or-take, there should be considerable cloudiness due to the proximity of the front to the north keeping temperatures from rising as much as neighbors to the south. Upper 30’s in this region should do with highs near freezing across the higher terrain.
The cold front stalls across the center of the region Saturday night. To the north of the front it will be cloudy and windy with scattered snow showers, especially across the higher terrain. Lows will fall into the singe digits and teens. To the south of the front skies will be partly to mostly cloudy, with increasing high clouds atop the lower level clouds towards daybreak as the storm moving out of the Gulf approaches. Lows will fall into the 20’s across the interior with 30’s along the coastal plain.
Mid-term - Issued - 1/15/10 @ 4:00pm
All attention shifts south on Sunday as the moisture-laden low pressure moving out of the Gulf of Mexico moves up the East Coast. There’s not much cold air ahead of this system in place over the Northeast as it approaches with 850mb temps across the southern half of the region in the 2-5°C range. The colder air across the north will more-or-less be held in place as the front separating this cold air across northern New York and New England from the remainder of the Northeast will be aligned to the upper-level flow aloft, allowing for little movement. Since phasing, which would draw down some of this colder air, isn’t likely to occur until later in the systems evolution and be limited at best as the initial batch of precipitation moves in it should be mainly in the form of rain. However, there is enough cold air that will be trapped in the low-levels across the interior for a mixed bag of sleet and freezing rain. This threat extends from central Pennsylvania, northeastward towards the Poconos and southern Catskills. Since this storm is originating from a very moist southern stream, drawing tons of Gulf moisture northward on a 50-60kt low-level jet, the rainfall could become heavy, especially along the coastal plain. This will occur by the afternoon as better lift/dynamics move into the region. Further inland, as this heavy precip moves in and temperatures aloft already slowly cooling due to evaporational cooling processes, the shot of stronger lift/dynamics should further cool the column allowing for precipitation to begin changing over to a heavy wet snow. Models are still on the fence with this one and a degree or two in either direction could mean the difference between nothing at all or a significant snowfall.
Precipitation continues across the region Sunday night, spreading northeast into New England during the overnight. Phasing with the northern stream will begin to occur, helping to draw in colder air from the north while dynamic/evaporational cooling processes continue. This effect will act to change rain over to snow across a wider portion of the interior during the evening and overnight hours on Sunday. Closer to the coast rain should dominate as temperatures both aloft and in the boundary layer stay above freezing. There may be a transition zone in there as well with some sleet and freezing rain with the best chances on Sunday night occurring across interior southern New England. The northward extent of the precipitation shield has consistently moved north with each ensuing model run and is now indicated to cover just about the entire region. Total QPF from this system should range from a tenth to a third of an inch across the far north with a third to three-quarters of an inch across the remainder of the interior. Along the coastal plain QPF should be three-quarters of an inch to an inch and a third. Temperatures Sunday night will be in the 20’s across the interior with 30’s along the coastal plain.
Fig.2 - Snowfall through Monday.
The storm will be moving out to sea on Monday, however, a weak northern stream low pressure will drift across the international border region bringing mainly light snow showers across the northern half of the region. Further south it will remain mostly cloudy. Temperatures may climb close to 40°F along the coastal plain with 20’s and 30’s over the interior.
Long-term - Coming later
Radar: Northeast Region Loop
Fig.3 - Radar loop of the Northeast region. Courtesy of Weather Underground.
Fig.4 - Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.
My weather dragon!
Updated: 4:29 PM GMT on January 17, 2010
By: sullivanweather, 5:46 PM GMT on January 10, 2010
Severe winter weather continues to make headlines but why has winter turned so harsh this year? Most in the US will see a break in one form or another this week but a weekend storm might bring another large snowfall from the Ohio Valley, northern Mid-Atlantic and Northeast.
Current watches, warnings and advisories.
Fig.1 - Current watches, warning and advisories issued by the National Weather Service. Courtesy of NOAA.
The highly anomalous high-latitude blocking pattern continues unabated into this second week of January 2010, similar to persistent blocking patterns observed during some very harsh winters during the 1960’s. As mentioned in the winter forecast, the winters of 1963-64 and 1968-69 have thus far served as great analogue years with many consecutive months of a –NAO index exhibited in those years, similar to this winter. Particularly cold and snowy weather have been plaguing many areas across central/eastern North America, western Europe and eastern Asia for 2-3 weeks straight.
Snowfall across the U.K. is being measured with meter sticks in some instances while European neighbors such as Germany and Poland aren’t only dealing with large amounts of snow but record breaking cold as well. The same holds true for such places as Beijing, China, where the combination of heavy snow and frigid temperatures had not been seen in half a century, and Seoul, South Korea where snowfall bested all-time records. Meanwhile here in the States we’ve dealt with a recently categorized NESIS-3 storm the week before Christmas across the Mid-Atlantic and Northeast Coast, a Christmas blizzard over the Plains and Midwest and now a week-long freeze across the Deep South. On the opposite end of the spectrum temperatures along the southern coastline of Greenland, due to persistent easterly winds of the Atlantic, have been warmer than those along the Emerald Coast of Florida and the French Riviera.
The ‘outbreak’ of severe winter weather can be traced to the end of the second week of December. At this time, some rather large tensions were beginning to build in the Northern Hemisphere circulation pattern as a strong blocking high-latitude ridge built over the far North Atlantic east of Greenland, represented by our old friend - a –NAO pattern. Additionally, the Arctic Oscillation (AO) was starting to tilt strongly towards the negative as well as the ridge building over Greenland spilled over the High Arctic. Working in conjunction with a modest sudden stratospheric warming event (SSW), this caused a split of the polar vortex into two vortices, one extending east-west from Finland to Siberia and the other over Nunavut. The final act was a wild swing in the global wind oscillation (GWO) through phases 6-7-8 of the WB (2009) GWO phase space diagram. What did this all mean?
Fig.2 - 4-month graph of the Arctic Oscillation Index. Note the 3-sigma anomaly in the index extending from the 2nd week of December until present time. (Credit: NOAA CPC)
As the NAO/AO becomes negative (high-latitude ridging) it forces the jet stream south as heights lower in the mid-latitudes in response; this gives a passageway for any airmass from the north to head south. Due to the SSW event, a large portion of the very cold air that normally sticks around over the North Pole had been displaced south, giving much more breadth to the coldest air over the Northern Hemisphere now covering the sub-arctic/northern mid-latitudes instead of the High Arctic – i.e. more cold air to tap. Now that there was very cold air to tap and it already had no trouble moving into the northern mid-latitudes due to the extremely anomalous high-latitude blocking expressed in the –NAO/AO pattern something had to push it further. In steps the GWO. The GWO moving through phases 6-7-8 aids in the process of southward momentum transport south of 35°N (phase 6) and mid-latitude cyclogenesis (phase 7). It’s no wonder why there was so much wintry weather across the mid-latitudes with so many variables that promote a cold and snowy pattern in place.
Fig.3 - GWO phase space centered on December. The swing to a high AAM over the two weeks from the 13-27th of December likely intensified mid-latitude storminess, helping to enhance an already notable negative AO index.
Fig.4 - 700mb anomalies over the two weeks spanning December 13-27th. (Credit: NOAA ESRL)
Closer to home, the biggest storm to strike the northern Mid-Atlantic since the President’s Day storm of 2003 occurred on the 19-21st, at a time when the MJO moved into phase 8 which promotes troughiness along the East Coast of North America. All of the above listed patterns and phases are called teleconnections in meteorology. Teleconnections are a very useful tool in weather forecasting as they are usually slower evolving than day-to-day weather and correlate rather well to regional patterns over the years. For example, it can take 3-5 days or longer for the MJO to move through one phase or 1-2 weeks for a PNA pattern to builds and break down. The NAO can stay persistent for months at a time or swing wildly from one phase to the next and back again over a fortnight.
Fig.5 - MJO phase space centered on December. Note the MJO was in phase 8 at the time of the East Coast blizzard, a favored phase for East Coast troughiness.
Recently there has been some relaxation of the extremely anomalous NAO/AO pattern over the northern hemisphere but teleconnections are still running 1-3 sigma anomalies and should continue to do so for at least the next week - more on that later.
Fig.6 - 700mb anomalies for the week of December 28, 2009 - January 3rd, 2010. (Credit: NOAA ESRL)
Focusing in on the Northeast at present and in the near-term, the region lies on the fringes of a sprawling arctic high pressure positioned over the nation’s midsection. Much colder air has funneled into the region over the past 24 hours on a constant northerly to northwesterly breeze. Despite the influence of the high most areas are seeing mostly cloudy skies, along with a few flurries around the Finger Lakes region and even south of Lake Champlain as the lake effect has been hard to tamp down, despite a strong low inversion. Temperatures will run in the teens and 20’s inland, with even a few single numbers for highs across the higher terrain of the North Country. Along the coast highs will be in the 20’s where some downsloping has broken the stratocumulus deck. Today’s temperatures are around 10-15 degrees below normal as we approach the climatologically coldest time of the year. Stratocumulus will break up some tonight but mid/high clouds will be on the increase ahead of a potent but moisture-starved shortwave progged to move through the region Monday and Tuesday. Lows will drop into the single digits and teens inland with upper teens to low 20’s along the coast.
The aforementioned shortwave moves though the region to start the work week without much fanfare. Snow showers and flurries will spread over the interior Monday with little to no activity east of the mtns until Monday night if at all. Accumulations should range from a dusting to an inch over the valleys with 1-3 inches across the higher terrain. Very early Tuesday morning a backdoor arctic front will slide across central/northern New England which may touch off some squalls and definitely bring in some much colder air for midweek across this region. Further south and west towards southwestern Pennsylvania the airmass will begin to moderate, now cut-off from the arctic air supply. Between these two areas, across New York/western New England, will be a tightening baroclinic zone that will serve as a conduit for an additional shortwave passage Wednesday that could bring more snow showers with very light accumulations. The real trouble may arise Wednesday night as warmer air begin to advect into the region as the flow turns west-southwesterly ahead of a northern stream system over Manitoba. This could lead to a period of light freezing drizzle across the interior of the Northeast. Refinement will definitely be needed here later. Otherwise, a continued moderation of temperatures for most of the region will occur except for northern New England stuck in the deep freeze with lows in the single digits.
The long-term starts out rather innocuous as the Manitoba low moves northeast to Hudson Bay trailing a cold front across the Upper Great Lakes region and into the Northeast Thursday and Thursday night. This may set off a few snow showers, primarily across the north with little accumulation. Further south this system will bring an increase in clouds and with a milder airmass in place lows should be some 5-10 degrees above normal. It won’t last long as cold air slowly bleeds into the Northeast on Friday as the cold front settles south. A second more powerful arctic front will arrive from the north Friday night with some bitterly cold air behind it. This will set the stage for the weekend as a moisture-laden southern stream storm will be moving northeast out of the Gulf of Mexico. Models are still undecided about this one but those pesky teleconnections signal a possible East Coast snowstorm. AO/NAO will still be at least one sigma in the negative as the MJO moves into phase 7/8, a position historically favorable to East Coast storminess. It’s going to come down to phasing and whether or not a northern stream disturbance can ‘catch’ the system moving out of the Gulf. If it does so there should be one mighty system somewhere over the southern US this weekend pulling northeast into an increasingly deeper arctic airmass. However the northern stream system might arrive too late and end up deflecting the system offshore the Southeast Coast. Operational models are trending towards a sheared system while the ensembles are showing a more robust storm. Over the last several weeks the highly anomalous pattern we’ve found ourselves in has given the ensemble solutions better verification over their operational cousin and I see no reason why this shouldn’t continue to be the case. Also given the operational models propensity to nudge systems northwest slowly over the days before its arrival also argues for a more developed/phased solution. Something to keep an eye on next weekend.
Looking ahead for the remainder of January a more –PNA pattern is forecast to develop as the AO/NAO continues to fluctuate on the negative side of things or even moving towards a neutral state. This could spell an end to the extremes in temperatures across the country but I wouldn’t be so fast to jump on that bandwagon. Persistence is a hard pattern to break and there’s every reason to believe this constantly negative AO/NAO could last all season. Plus the extensive cold snow cover across the country should stave off a rapid warm-up. Should a –PNA pattern develop as suggested by model guidance a return to storminess and high precipitation events should occur across the country during the last 10 days of the month spreading east from California.
Radar: Northeast Region Loop
Fig.7 - Radar loop of the Northeast region. Courtesy of Weather Underground.
Fig.8 - Sea-surface temperatures off the Northeast Coast. Courtesy of NOAA.
My weather dragon!
Updated: 6:19 PM GMT on January 10, 2010