Summary: The pesky upper-level cold pool (low pressure) which has been rotating above us for the past several days, reminding us either of why we love winter, or why we want winter to end, will finally weaken and drift eastward on Tuesday. One last disturbance, rotating around the cold pool, will give us one last bout of snow flurries/showers tonight. Our weather will then improve a bit tomorrow as the northwest winds finally die down, temperatures rise slightly (almost normal) and we may, may actually see a little of the sun during the afternoon. The big forecast question then will become: How will the mid-week coastal storm affect Berkshire County?…..
Divergence of the upper-level flow associated with a strong disturbance in the jet stream, diving south out of the upper Great Plains today, is generating ascent in the atmosphere above a developing surface low pressure system in the central Great Plains. This “dynamic” weather system will progress slowly eastward over the next two days, with the surface low centered over West Virginia by Tuesday evening. Overnight Tuesday this “primary” surface low will weaken as it begins to lag behind its upper-level support and a new, “secondary” surface low will develop off the Mid-Atlantic Coast as the upper-level energy moves out over the warm waters of the Gulf Stream. During the day on Wednesday, the surface low will begin to deepen (intensify) as the trough in the jet stream containing the previously mentioned upper-level disturbance becomes negatively tilted, enhancing the divergence in the jet stream flow. The increasing ascent in the atmosphere (which generates the clouds and precipitation) will be enhanced further by increasing environmental instability (warm at surface [Gulf Stream], cold aloft [the “upper-level disturbance” is a cold pool aloft]). Bottom line: There will be a broad swath of fairly heavy snow accumulations, 6-12″ or so along the path of the surface low from the upper Great Plains trough the Midwest and into the Mid-Atlantic states. As the low intensifies off the coast on Wednesday, precipitation will be enhanced and heavy, wet snow could really begin to pile up over the mountains of West Virginia, eastern Kentucky and western Virginia, with snowfall totals well over one foot. Heavy wet snow will also likely pile up in the Baltimore and Washington, D.C. areas but this will likely be likely be limited, in D.C. in particular, since they will be right on the snow/rain line and it will probably rain for a while before changing to snow. However, given how wet the snow will be, and because winds will be picking up as the surface low strengthens, I suspect power outages could become quite widespread across these regions.
All of the computer models pretty much agree on the preceding scenario. However, beyond this point there is disagreement as to the track along the coast and its impact on New England. As I suspected, all of the models have had a bit of a northward drift in their storm track over the past few days. All of the models have the storm weakening as it drifts slowly eastward off the Mid-Atlantic Coast, as it moves directly under the upper-level cold pool (so that it becomes “cut-off” from its upper-level support) and is prevented from moving up the coast by a blocking upper-level ridge (warm pool) over eastern Canada. “Cut-off” high pressure like this is more unusual than the more common cut-off lows, but they do occur more commonly than people realize.
However, the models differ on the exact track of the low and its impact on New England. The European model (ECMWF) has been quite consistent from run to run, with a slight northward drift in the track with each run. This model presently has us getting brushed by the northern edge of the precipitation shield late Wednesday night and into Thursday morning as the surface low drifts due east, well off the Mid-Atlantic Coast, giving us little, if any, snow accumulation. The greatest likelihood of accumulation would be in South County. This model actually gives us the greatest likelihood of accumulation from some wrap around moisture on Friday as a disturbance circulates back over us from the cut-off low over the ocean. This would still only amount to an inch or so at most. The U.S. higher resolution NAM model has had a much less stable outcome from run to run but the latest run has come into line with the ECMWF model. However, this model tends to be the not particularly reliable with East Coast snowstorms. The U.S. GFS model (fairly reliable with these scenarios, but not as consistently good as the ECMWF) has been all over the place. One run the storm misses us, the next run we get crushed. In this morning’s run the surface low drifts much further northeast than the other models, right off Cape Cod, and we get a foot of heavy, wet snow.
Although the ECMWF has been better this winter than the GFS, the northward trend in the track of the storm over the past several days’ model runs is more consistent with my gut feeling about this storm from my past experience and I think there is a significant possibility that we could get a heavy, wet March snowstorm Wednesday night into Thursday.
Bottom line: We may only get brushed by the storm and receive a few bothersome inches of wet snow Wednesday night into Thursday morning. However, my tendency right now is to lean toward the possibility that we could receive a more significant heavy, wet snowstorm. I will post an update tomorrow afternoon….
Unfortunately, the northwest flow around the resulting cut-off low will drag chilly air down over New England and prevent the warm-up late this week and this weekend that I had hoped for last week. It does appear, however, that we may get sunny weather this weekend with temperatures possibly reaching the 40s as surface high pressure builds in.
Monday Night
Mostly cloudy to overcast with a period of snow showers likely this evening. Probability of precipitation 60%. There will likely be a dusting in a few locations, and up to 1/2″ in a few spots over the elevated terrain. There is just a chance of a snow shower after midnight. Probability of precipitation 30%.
Low temperatures generally near 20 to low 20s, upper teens over the elevated terrain.
Northwest winds at 10-15 mph, diminishing a bit toward morning.
Tuesday
Mostly cloudy with a few sunny breaks. It may actually become partly sunny for a time during the afternoon, particularly in South County.
It will be slightly milder than recent days, with high temperatures in the mid to upper 30s in Pittsfield, Adams, North Adams and Williamstown, upper 30s in Great Barrington and Sheffield, and low 30s over the elevated terrain and hilltowns.
Northwest winds at 5-10 mph, becoming northerly in the afternoon.
Tuesday Night
Becoming overcast with a chance of snow showers, particularly after midnight. Probability of precipitation 30%. Nothing more than a dusting.
Low temperatures in the upper 20s in most locations, mid 20s over the elevated terrain.
Light north-northeasterly winds in the evening, shifting to east-northeasterly and increasing to 8-12 mph by morning.
Wenesday
Mostly cloudy in the morning, becoming overcast in the afternoon. There is the good chance of light snow or snow showers, predominantly over the elevated terrain to the east. There is the chance that a steadier snow could develop toward evening. Probability of precipitation 60% over the elevated terrain to the east, 50% elsewhere. A coating to 1″ could fall in the elevated terrain, a coating to 1/2″ elsewhere.
High temperatures in the mid 30s in Pittsfield, Adams, North Adams, and Williamstown, mid to upper 30s in Great Barrington and Sheffield, upper 20s to low 30s over the elevated terrain (depending on elevation).