The following forecast is provided by Joe Kravitz, the instructor for the Introduction to Meteorology course, since there are no classes at BCC today due to Thanksgiving break:
Summary: We are in for a shock this weekend as a strong cold front will move through the region this evening and finally end our long period of fair weather and above average temperatures, giving us our first real taste of winter.
The jet stream wave pattern has become more amplified and a cold trough (southern dip in the jet stream) is presently plunging southeastward through the upper Midwest and Great Lakes. The leading edge of this trough is manifested at the surface as a strong cold front.
Just a note, the jet stream is just the manifestation at the tropopause (upper boundary of the troposphere, the lowest layer of the atmosphere where all the up and down motion in the atmosphere, and thus, weather occurs) of the “polar front”, the semi-permanent boundary in middle latitudes (30-60 degrees) where the strongest temperature contrast between cold air to the north and warm air to the south exists.
Even though there is significant lifting associated with the front due to the pronounced temperature difference across the front, the front has limited moisture to work with (surface dew points in the low 30s) so there will only be scattered light rain showers these evening until about 2 am. Any showers will initially be in liquid form but there may be a change to snow showers/flurries around midnight, following frontal passage. However, any snow that falls will not accumulate.
Once the cold front passes, we will remain in the colder air to the north of the jet stream for quite some time, probably through at least next week. Therefore, temperatures will generally be below average. In addition, our surface winds will shift to the west/northwest and become quite strong over the course of the weekend. This will result in quite low wind chill temperatures. Also, at this time of year, the Great Lakes are still quite warm so that as the cold air behind the front blows over the warmer water, the atmosphere will destabilize and clouds and lake-effect snow showers will develop. Most of this snow will fall over western and central New York state. However, we will be at risk of a few scattered lake-effect snow showers/flurries in the Berkshires as well. It is sometimes not well known that even though most of the moisture which evaporates from the lakes in these scenarios falls as precipitation before it reaches us, any moisture that remains can condense into clouds and, sometimes, precipitation as the air is lifted by the Taconic and Hoosac ranges as it ascends out of the Hudson Valley to our west. We are, in effect, the “last stop on the lake-effect train”.
A very weak disturbance in the jet stream will ride southeast out of Alberta, manifested as a weak surface low pressure system (“Alberta Clipper”) over the weekend and reach us Sunday night. The surface low will weaken considerably and dissipate over the Northeast on Sunday night. The “lifting” in the atmosphere associated with this process may give us a some scattered snow showers late Sunday afternoon and Sunday evening but there should be little, if any, accumulation.
A more significant storm may move through our region Tuesday into Wednesday. The two main long-range models, the U.S. based GFS model and the European based ECMWF model are quite divergent in their outcomes for this storm. Both models have us remaining in the cold air so any precipitation we get is likely to be snow. In addition, the trend has been toward a colder storm. The ECMWF model presently has the storm moving out to sea well to our south and east on Tuesday. However, this model has been very inconsistent with the track and, even though this model has had a better track record, given the inconsistencies between runs, I have a low confidence in this model at this point. The GFS has been much more consistent and I find its outcome more realistic. However, the track of the storm even with this model has been trending south and east with the track to our northwest a few days ago (mixed precipitation for us) and now to our southeast, moving off the New Jersey coast and over Cape Cod (all snow). The trend has also been to a weaker storm with both models. So, at this point, I think the most likely scenario is a light to moderate snowfall from Tuesday into Wednesday. I will update this tomorrow….but for now, get ready for much more winter-like weather this weekend. I suspect it will be a shock to the system for most people given our recent mild and tranquil weather.
Friday Night
Increasing clouds with the good chance of scattered rain showers this evening. Any rain showers will likely mix with and change to snow showers by midnight, particularly over the elevated terrain. However, there will be little or no accumulation (dusting over the higher terrain, at best). Most shower activity will end by 2 am. There will be partial clearing in some areas toward daybreak. Probability of precipitation is 50%. Melted liquid precipitation totals will be less than 0.05 inches in most locations.
Temperatures will fall steadily overnight, reaching near 30 in most locations by daybreak. Low temperatures will only be in the low 30s in some parts of South County and the upper 20s over the elevated terrain.
Southerly winds at 8-12 mph this evening will shift to west-northwest and increase to 10-15 mph around midnight, as the cold front moves through.
Saturday
It will average out partly sunny (50-75% cloud cover) in the morning, but become mostly cloudy during the afternoon. It will be windy and much colder. There is the chance of scattered snow showers/flurries. The best chance for snow shower activity appears to be during the early morning and late afternoon, but a snow shower could occur at any time. Probability of precipitation will average 40% but will be higher in the elevated terrain. There will be little or no accumulation in most locations, although there could be a dusting in some heavier snow showers, particularly over the elevated terrain.
Temperatures will rise little over the course of the day as cold air rushes in from the northwest. High temperatures will be in the low to mid 30s in Pittsfield, mid 30s in Adams, North Adams and Williamstown, mid to upper 30s in South County, and upper 20s to low 30s over the elevated terrain and hilltowns, depending on elevation. Wind chill temperatures will be as low as the upper teens when the wind gusts, but will average in the low to mid 20s.
West-northwesterly winds at 15-25 mph with gusts to 35 mph, particularly in the elevated terrain.
Saturday Night
Mostly cloudy with a chance of a snow shower/flurry, mainly before midnight. Probability of precipitation 40%. Little or no accumulation. Becoming partly cloudy after midnight. Windy and cold.
Low temperatures in the low 20s in most locations with upper teens over the elevated terrain. Wind chill temperatures in the single digits.
West-northwesterly winds at 15-25 mph with gusts to 35 mph.
Sunday
Partly sunny in the morning. Cloud cover will be mostly, relatively thin mid and upper level clouds. However, clouds will lower and thicken late morning through the afternoon. There is a chance of a snow shower late afternoon. Probability of precipitation 30%.
It will remain windy and cold. High temperatures in the low 30s in Pittsfield, low to mid 30s in Adams, North Adams and Williamstown, mid 30s in South County and upper 20s to low 30s over elevated terrain and the hilltowns, depending on elevation. Wind chill temperatures will again be between the upper teens and mid 20s.
North-northwesterly winds at 15-25 mph will begin to diminish and shift to the southwest late.