Berkshire County Forecast-Thursday, December 20

The following forecast is provided by Joe Kravitz, the  instructor for the Introduction to Meteorology course:

Summary: After our one nice day today, the storm which is presently giving the upper Midwest a large snowstorm will move through our region tonight and Friday. As with previous storms this year, the surface low pressure center will track to our northwest, leaving us on the warm side of the storm/jet stream. As a result, we will again receive mostly rain, and a fairly substantial amount. This storm, however, is a little different than our previous one. It is much stronger, with a lower central pressure (~980 mb) and, therefore, has a very tight pressure gradient surrounding it. The resulting strong pressure gradient force (PGF) will generate very strong winds. Also, as the surface low drifts by just to our northwest, it will drag its trailing cold front across the region and then slow down and, essentially, stall over northern New England on Friday night and Saturday. The strong, cold, west-northwest winds circulating around the back side of the low will move over the warm, unfrozen Great Lakes, resulting in evaporation of large amounts of moisture and generate large amounts of instability in the atmosphere (warm near the surface/much colder aloft) above the lakes. This will result in considerable upward movement of the moisture laden air that will be enhanced by convergence at the surface as the air reaches the eastern shores of the lakes and surface friction increases (air slams on the brakes and “piles up”). The upward movement will be enhanced even further by the elevated terrain in upstate NY. Upward motion in the atmosphere leads to cooling, condensation (cloud formation) and, eventually, precipitation. The stronger the upward motion, in general, the heavier the precipitation. The last few sentences were a description of how “lake-effect” snow forms and this is shaping up to be a major lake-effect snow event for upstate NY. Some regions will likely receive in excess of a foot of snowfall. Most of this lake moisture will fall as snow before it reaches Berkshire County, however, we will still get some lake-effect snow showers Friday night and Saturday. The lower elevations will likely receive a dusting to 1″ with 1-3″ accumulating over the elevated terrain.

The surface low will weaken considerably over the weekend as it becomes separated from the jet stream and drifts slowly over the Canadian Maritime on Sunday. However, for the first time this season, the jet stream will move south of the region and we will have normal to slightly below normal temperatures for several days. A very weak disturbance passing by to our south on Monday night and Tuesday may give us a little light snow or snow flurries but it does not look like much, if any, accumulating snow at this point. The long-range models are generating a strong surface low pressure system along the East Coast next Thursday but it is too early to tell if this potential storm will impact us and, if so, what type of precipitation we will get.

Thursday Night

Increasing clouds this evening, becoming overcast by late evening. Scattered light snow showers will likely develop near midnight and transition rapidly to sleet and, eventually rain by the early morning hours. No snow accumulation is expected in most locations although there could be a dusting over the elevated terrain before the changeover. Rain will become steadier and heavier toward daybreak. Probability of precipitation near 100%. Rainfall totals between 0.25″ and 0.50″. It will become windy toward morning.

Temperatures rising gradually after midnight to the upper 30s to near 40 in the lower elevations and mid to upper 30s over the elevated terrain.

East-southeast winds at 5-10 mph this evening will increase after midnight, reaching 15-25 mph by daybreak with the stronger wind speeds over the elevated terrain. Gusts to 40 mph, greater over the higher terrain, are possible.

Friday

Rain, heavy at times, through the morning. Rain should end by early afternoon. Probability of precipitation near 100%. Rainfall totals between 0.75″ and 1.00″. There will likely be some breaks in the overcast during the afternoon. It will be quite windy in the morning but winds should die down slightly in the afternoon after the cold front passes. It will be mild in the morning but turn colder during the afternoon.

High temperatures will be late morning to early afternoon, with low 40s in Pittsfield, Adams, North Adams and Williamstown, low to mid 40s in Great Barrington and Sheffield, and upper 30s in the elevated terrain and hilltowns. Temperatures will fall into and through the 30s during the afternoon after the cold front passes in the early afternoon.

East-southeast winds at 15-25 mph, 20-30 mph over the elevated terrain, with gusts between 40 and 50 mph likely in the morning til early afternoon. Winds will then shift to the southwest and decrease somewhat, to 10-20 mph during the afternoon.

Friday Night

Overcast with scattered snow showers developing during the evening, becoming more widespread well after midnight. Probability of precipitation 70%. Snowfall totals for Friday night and Saturday combined will be a dusting to 1″ in the lower elevations and 1-3″ over the elevated terrain and hilltowns.

Temperatures falling into the upper 20s by morning, mid 20s over the elevated terrain.

Southwest winds at 8-12 mph becoming west-northwesterly toward morning.

Saturday

Overcast with scattered snow showers, breezy and colder. Probability of precipitation 70%. Snowfall totals for Friday night and Saturday combined will be a dusting to 1″ in the lower elevations and 1-3″ over the elevated terrain and hilltowns.

Temperatures will not rise much over the course of the day with high temperatures in the low 30s in Pittsfield, low to mid 30s in Adams, North Adams and Williamstown, mid 30s in Great Barrington and Sheffield, and upper 20s in the elevated terrain and hilltowns.

West-northwest winds increasing to 10-20 mph with gusts to 30 mph.