Note: Clicking on underlined red text provides links to various weather maps. I will be unavailable to update this forecast until Sunday afternoon.
Summary: A broad and deep trough in the polar front jet stream is now overlying a substantial portion of the central and western U.S.. This has permitted a very cold arctic air mass for this time of year to sink south over the Great Plains and upper Midwest. This type of air mass this early in the season has been unusual in recent years (global warming?). High temperatures in portions of the upper Great Plains are below zero and even in the teens below zero today. The cold air has spilled west all the way to the west coast where there were freezes in the central valley of California this morning and afternoon temperatures are having trouble reaching 50 degrees, even along the coast in San Francisco.
The cold front at the leading edge of this trough will sink slowly southward through our region over the next 24-36 hours as the trough inches south and east. Two disturbances, along with their accompanying batches of precipitation, will ride along this front as it moves through. As a result, we will have rain tonight into tomorrow morning. There will then be somewhat of a pause in the precipitation later tomorrow morning into the afternoon. The second disturbance will then move through later Friday afternoon through a good part of Friday night. By this point, colder air behind the front will be moving in and there will be a transition from rain in the mid-afternoon to freezing rain and sleet late afternoon into the evening. Roads may become slippery for the afternoon/evening commute. Sleet should change to snow over the course of the evening. It is difficult to pinpoint the changeover time. Some models suggest the vertical temperature profile will be consistent with snow as early as 6 or 7pm with others suggesting a changeover by 8 to 10 pm. The snow should then continue for several hours and then begin to taper off after midnight. Snowfall accumulations are highly dependent on the changeover time but it appears that 3 or 4 inches is a pretty good bet with as much as 6 inches over the elevated terrain if the changeover occurs early in the evening.
Skies should begin to clear on Saturday afternoon as we have a colder, somewhat blustery day as surface high pressure builds in. The coldest of the arctic airmass should remain well to our west, for the time being, as temperatures reach the low 30s on Saturday and near 30 in most areas on Sunday. The cold front will remain stalled well to our south over the weekend as high pressure builds in. However, another surface low pressure system will develop along the front and begin to push the front back towards us a warm front. The front will move through on Monday as the center of the surface low moves by to our west and dissipates as a secondary low forms along the coast and moves out to sea. Right now it looks like 2-4″ of snow after midnight on Sunday into mid morning Monday with a changeover to sleet and freezing rain mid-morning on Monday with just some leftover light rain and drizzle in the afternoon. I will update this portion of the forecast on Sunday afternoon.
As this “last” storm pulls away, the deep trough will shift east, allowing the arctic air mass to our west (which will be reinforced with more arctic air from Canada) to finally move over our region by mid-week. It is possible that high temperatures will barely reach the teens by Wednesday or Thursday. (OUCH!)
Thursday Night
Occasional rain. Rain will likely be heaviest and steadiest after midnight. Probability of precipitation near 100%. Rainfall totals near 0.25″.
Steady temperatures near 50 before midnight, falling rapidly after midnight. Low temperatures in the upper 30s by morning, mid 30s over the elevated terrain.
Southwesterly winds at 5-10 mph, shifting to northwesterly after midnight.
Friday
Rain likely early in the morning with a bit of a break from late morning through mid-afternoon and then picking up again late afternoon. The rain may change to sleet and freezing rain late. Probability of precipitation 90%. Rainfall totals near 0.25″.
Temperatures will hold steady in the upper 30s, mid 30s over the elevated terrain for most of the day and then fall toward or to freezing by nightfall.
Northwesterly winds at 8-12 mph.
Friday Night
Freezing rain and sleet changing to snow during the evening. The changeover will likely occur earlier in northern parts of the county but there should be snow everywhere by 9 or 10 pm. There could be some icing, 0.10″ or so before the changeover, particularly in South County. Snow will begin to taper off after midnight. Snowfall totals will most likely be in the 2-4″ range with as much as 6″ over the elevated terrain in central and northern Berkshire.
Low temperatures in the mid 20s, low 20s over the elevated terrain.
Northwesterly winds at 5-10 mph.
Saturday and Saturday Night
Mostly cloudy in the morning with the chance of a lingering flurry early. Partly sunny during the afternoon with a chance of a late afternoon or evening lake-effect snow shower. Nothing more than a dusting. It will be breezy and colder. Variably cloudy, breezy and cold overnight.
High temperatures in the low 30s in Pittsfield, Adams, NorthAdams and Williamstown, Lee and Stockbridge; low to mid 30s in Great Barrington and Sheffield and: upper 20s over the elevated terrain. Low temperatures overnight in the low to mid teens.
West-northwesterly winds at 10-15 mph with gusts to 25 mph, diminishing to 5-10 mph overnight.
Sunday
A veil of high, thin clouds may dim the sun in the morning. Increasing clouds in the afternoon. High temperatures will average around 30.