The short-term forecast for Berkshire County (next few days) has not changed since yesterday [cold, breezy, mostly cloudy and scattered lake-effect snow showers through tomorrow] and so I will not submit a “full” forecast until tomorrow. However, the scenario is beginning to look much more interesting for this weekend so I would like to discuss that. As I mentioned in yesterday’s forecast, a trough in the jet stream wave pattern moving out from over the Rocky Mountains is generating a surface low pressure system over the Great Plains that will result in heavy snow for Kansas, Nebraska and Iowa tonight and tomorrow. The trough is not particularly deep (the jet stream wave pattern is fairly zonally (west-east) oriented [not particularly amplified]) and so the dynamics are not particularly strong with this storm. Therefore, the surface low will be fairly weak and winds will be relatively light and the air is not particularly cold so this will not be a classic Great Plains “blizzard” with very strong winds, reduced visibility and frigid temperatures that is typical of this region with featureless terrain and access to arctic air from Canada. However, as is becoming fairly typical for this winter, snowfall totals will be very heavy (over one foot) because of large amounts of moisture (water vapor) in the atmosphere associated with this storm [global warming?].
As the trough propagates eastward, it will “flatten out” even more, and the surface low will weaken rapidly and, essentially, dissipate as it moves into the Great Lakes Friday and Saturday. However, an upper-level disturbance (counterclockwise rotating cold pool aloft associated with a jet “streak” [short burst of particularly strong jet stream winds] will rotate through the base of what remains of the trough as it approaches the East Coast on Saturday. Yesterday it appeared that this disturbance was not as strong as it looks in all of the computer model runs today and I was skeptical that we could get much in the way of a snow storm this weekend. However, it now looks like, even though the jet stream pattern will remain un-amplified (NOT a typical scenario for a big East Coast snowstorm) the strong disturbance will create a sharp “kink” in the trough as it moves over the coast on Saturday. This, if it occurs, will create large amounts of divergence in the jet stream winds that will essentially “suck” air out of the atmospheric column below it. This will create strong upward motion (rising, cooling and condensing air) which likely will result in an area of heavy precipitation and surface low pressure off the Mid-Atlantic Coast. In addition, as with the last snowstorm, as the cold pool aloft moves over the warm Gulf Stream the upward motion will increase (due to environmental instability) and this may enhance the upward motion further. On top of this, there will be plenty of moisture available for evaporation from the Gulf Stream as the storm gets going.
The configuration and dynamics of this storm do not appear as prodigious as the one that crushed southeastern New England earlier so I do not see there being nearly as much snow with this storm. However, the storm looks to track closer to the coast and Berkshire County may get as much as with that storm. However, we will be close to the snow/rain line with this storm (although it looks like all snow for us right now) so with temperatures near freezing the snow will be “wetter” which should hold down accumulations.
Bottom line: Snow developing sometime Saturday afternoon or evening and continuing, heavy at times, into Sunday. Most likely accumulation, right now, looks like about one foot. CAVEAT: I do not feel this is a high confidence forecast at this time. This is not the classic appearance of a big snowstorm for Berkshire County, even though the models seem to be converging on this result. This scenario will likely change over the next few days so I will continue to update each day…..