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Summary: Even though the U.S. computer models have been all over the place with Thursday’s storm (or lack there of), they are finally beginning to converge on the solution that the European Model (ECMWF) has been very consistent with for several days now. Therefore, although there are still important difference’s between the models, I am tempted to find the ECMWF solution more reliable at this point. First, let me lay out what all of the models are agreeing upon…..

A weak surface low pressure system, presently developing over the Gulf of Mexico, will drift slowly northeastward to a location along the southeast U.S. coast Wednesday evening. The low will then drift more northerly to a position right over Cape Hatteras, NC by Thursday morning. At this point, the low will still be fairly weak with a central pressure near 1000 mb. However, it will be carrying loads of moisture from the Gulf of Mexico and Gulf Stream so it will have already wreaked havoc on the Southeastern states with large amounts of wintertime precipitation that they are unaccustomed to (hopefully lessons will have been learned from the snow “storm” in Georgia a few weeks ago). In particular, the southern Appalachians will likely receive over a foot of heavy wet snow during this time.

During the period from now until Thursday morning the trough in the jet stream configuration responsible for generating this surface low will become more amplified and during the day on Thursday it will become “negatively tilted”. This configuration will create a large amount of “divergence” of the jet stream winds above the surface low that will enhance the upward motion and deepen the surface low. As a result, the storm will undergo rapid development as it moves northeastward along the Mid-Atlantic and New England coast, attaining a very low central pressure around 970 mb by the time it reaches the Gulf of Maine Friday morning.  Therefore, precipitation will become heavy, winds will strengthen, particularly along the coast, and there will likely be some coastal flooding Thursday and Thursday night in the Mid-Atlantic states and New England.

The million dollar question is…where will the heaviest precipitation fall and it what form? This is where there are important differences between models. There will be a band of heavy snowfall which will have a very sharp northwestern margin with a changeover to sleet and freezing rain to the southeast of the band. The U.S. models track the surface low off the coast, moving southeast of Cape Cod. These models also move the low relatively quickly so that precipitation will begin here near daybreak but end during the evening on Thursday.  This track would keep most of New England cold enough at all levels of the atmosphere so that snow would fall everywhere except Cape Cod. In this scenario, the band of heaviest snow, over one foot and possibly well over, would fall to the southeast of Berkshire County. In addition, the northwestern edge of the heavier snow would lie right across Berkshire County for much of the storm. If this scenario was realized, the northwest corner of the county (e.g. Williamstown) would receive about 4-6″ of snow and the elevated terrain to the southeast (e.g. Otis, Becket, Sandisfield) would receive near 12″ with amounts elsewhere in the county increasing in amount from northwest to southeast between these two locations.

The ECMWF model scenario differs somewhat. It has consistently tracked the surface low more slowly and had it hugging the coast closely, moving directly over southeast MA. In this scenario, the heaviest band would lie over southeastern parts of Berkshire County during the day Thursday with enough warm air off the ocean overriding the cold air at the surface to possibly change the precipitation to sleet there briefly sometime during the afternoon or evening before changing back to snow. This track could also enable the “dry slot” (dry air wrapping into the low) to move over Berkshire for a time. A band of “backlash” snow would then rotate through the county Thursday night, affecting northern portions of the county to a greater extent, with snow not ending until well after midnight on Thursday night.

So, enough blather, what do you think is going to happen? You’re a meteorologist, make a forecast already!

I think the most likely scenario at this point is that snow will develop across Berkshire County from south to near daybreak Thursday morning. The snow will likely be light at first but become moderate to heavy at times, particularly  in central and southern portions from mid morning through the afternoon. The snow may change to sleet briefly in the south late in the afternoon. I would expect the snow to lighten or end for a time during the evening with mostly light snow, with some heavier bands, redeveloping later in the evening. This backlash should have its greatest impacts over the elevated terrain, particularly in North County. Snow should end sometime after midnight, probably during the early morning hours. Predicting snow fall totals is almost a guess at this point but I think we are in for a substantial snowfall, with 8-12″ likely for most of the county. However, I would not be surprised to see over a foot, maybe well over a foot in the elevated terrain, if the cards all align right (wrong). I will update this forecast late tomorrow afternoon. Hopefully, the forecast will have a higher degree of certainty at that time. However, my gut tells me that we won’t have a definite answer until the snow ends with this one. One thing I do know with a fairly high degree of certainty is that there will be places in the Appalachians and along the east coast that receive more than a foot of snow from this storm.

Tuesday Night

Mostly clear and very cold.

Low temperatures in the single digits below zero. Most locations will be in the mid single digits below zero but some valleys, particularly over the elevated terrain, could fall to -10° F.

Northwest winds at 5-10 mph this evening, becoming light after midnight.

Wednesday

Sunny skies, except for a thin veil of high clouds at times during the afternoon. Still cold, but not quite as cold as the past few days. In particular, it will feel milder since winds will be light and the sun is fairly strong in mid-February.

High temperatures in the low 20s in Pittsfield; low to mid 20s in Lee, Stockbridge, Adams, North Adams and Williamstown; mid 20s in Great Barrington and Sheffield and; upper teens to near 20 over the elevated terrain.

Winds light and variable.

Wednesday Night

Increasing clouds with snow likely developing from south to north near daybreak. Probability of precipitation 60%. 1″ or less accumulation by 8 am.

Low temperatures in the low to mid teens during the evening, rising to near 20 by daybreak.

Southeast winds at 5-10 mph, shifting to northeast after midnight and increasing to 10-15 mph by morning.

Thursday and Thursday Night

Snow and becoming windy. Snow will likely be moderate to heavy at times from mid-morning into the evening. There may be a brief changeover to sleet in southern portions late afternoon or early evening. Likely snowfall totals by evening 6-10″. Snow will lighten or end for a time during the evening. Light snow with a few moderate bursts will likely re-develop later in the evening ending after midnight. Most likely total snowfall accumulations 8-12″ although greater amounts are possible.

Daytime high temperatures low to mid 20s in most locations, upper 20s over South County and near 20 over the elevated terrain. Temperatures only falling a few degrees overnight, ranging from upper teens to low 20s by morning.

Northeast winds at 10-15 mph during the morning, shifting to northerly and increasing to 15-25 mph during the afternoon, shifting to northwesterly at 15-25 mph during the evening and decreasing to 10-15 mph after midnight.