Summary: I thought it was safe to take a deep breath but…..another complex storm system is headed our way. In fact, this system is very complex. The most difficult forecast for a meteorologist to make at this time of year is precipitation type. With this system, Berkshire County will sit right on the boundary between various precipitation types for a prolonged period, starting near midnight Tuesday night. The precipitation intensity will be greatest overnight Tuesday into Wednesday afternoon. However, the event will linger with off and on light precipitation right into Thursday. The forecast that I make today will be fairly low confidence in regard to precipitation type. This will evolve over the next day, becoming a higher confidence forecast tomorrow afternoon as we get closer to the actual event….

A surface low pressure system presently over the southern Great Plains, which is battering them with another round of heavy snow, will move slowly northeast, towards the Great Lakes over the next 2 days. As it drifts northeastward it will weaken considerably as it looses its upper-level (jet stream) support (divergence). Its cold front and warm front will merge to form an occluded front as the storm undergoes a SLOW demise. This occluded front will approach our region overnight Tuesday with an array of precipitation types as milder air overruns colder air near the surface. It will likely start as a little light mix just before midnight and then turn to snow as the precipitation intensity increases and evaporation from the falling precipitation cools the air aloft to below freezing. There then will likely be a period of snow from just after midnight into Wednesday early morning. Sometime Wednesday morning, it is difficult to say when at this point, probably between 7 and 10 am, the milder air (finally above freezing) will move in aloft and the precipitation will turn to sleet (ice pellets) and, probably fairly quickly after that, to freezing rain (rain falling into below freezing air near the surface so the rain freezes on contact with surfaces). The precipitation will eventually change to just plain rain in the lower elevations as surface temperatures rise above freezing late morning to early afternoon. It will likely stay freezing rain in the elevated terrain. The rain (both freezing and plain) should begin to taper off early to mid-afternoon.

The snow accumulation forecast for Tuesday night into Wednesday morning is low confidence and depends on the timing of the changeover to sleet and rain. My best estimate right now would be 2-4″, with the lower amounts more likely in the lower elevations and the greater amounts more likely in the elevated terrain. There could be as much as 0.10″ of freezing rain in the lower elevations (followed by about 0.20-0.30″ plain rain) but as much as 0.30-0.40″ in the elevated terrain during the day on Wednesday. However, even though air temperatures may be below freezing, they will be close to freezing and the high sun-angle this time of year should help limit ice accumulation.

During the day on Wednesday, a new weak surface low pressure system will develop off the New Jersey coast, along what is called the “triple point”, where the occluded front extending eastward from the original surface low merges with the original warm and cold fronts. As this occurs, the wind will begin to shift from easterly to northeasterly (counterclockwise circulation around low pressure). This wind flow will likely bring colder air back in aloft so that the precipitation changes back to snow overnight Wednesday. Snow should be light, however, and only accumulate an inch or two overnight and into Thursday. On Thursday, we may have another burst of snow (another inch or so) as the whole system drifts slowly east and the upper-level low (cold pool) moves over the region and de-stabilizes the atmosphere somewhat.

No matter how this turns out it should be a mess for Berkshire County with several inches of snow likely on the ground on Wednesday morning with a transition to sleet and freezing rain likely occurring at some point during the morning. I will update this forecast tomorrow afternoon……

Monday Night

Partly cloudy, calm and fairly mild for this time of year.

Low temperatures in the mid 20s in most locations, with some low 20s over the elevated terrain.

Light northwesterly winds this evening, becoming calm after midnight.

Tuesday

Mostly sunny in the morning, increasing clouds during the afternoon.

Temperatures will be seasonable, with high temperatures in the upper 30s in Pittsfield, near 40 in Adams, North Adams and Williamstown, low 40s in Great Barrington and Sheffield, and low to mid 30s over the elevated terrain and hilltowns (depending on elevation).

Light east-southeast wind in the morning, increasing to 5-10 mph during the afternoon.

Tuesday Night

Becoming overcast during the evening with a little light mixed precipitation likely just before midnight. Any mixed precipitation will change to snow and increase in intensity after midnight. Snow, moderate at times, after midnight. Probability of precipitation near 100%. Most likely snow accumulations 2-4″ with the greatest amounts over the elevated terrain.

Low temperatures in the upper 20s to near 30 over the lower elevations and mid to upper 20s in the elevated terrain.

Easterly winds at 10-20 mph, increasing to 15-25 mph after midnight. Winds will increase within this range with increasing elevation. Gusts between 30 and 40 mph are likely after midnight, particularly over the elevated terrain.

Wednesday

Snow in the early morning will likely transition briefly to sleet and then to freezing rain early to mid morning. Most likely time for this transition looks to be between 7 and 10 am. Freezing rain will likely change to rain in the lower elevations by mid to late morning and icing will likely not be a major problem there. It will likely remain freezing rain over the higher elevations. However, as noted in the summary, even though as much as 0.30 -0.40″ of freezing rain could fall in the higher elevations, with temperatures near freezing, the high sun-angle should help limit ice accumulations. Freezing rain and rain will begin to taper off during the early to mid afternoon. Probability of precipitation near 100%. Additional snowfall accumulation during the morning less than an inch. Total rainfall (both freezing and plain) around 0.30 – 0.40″.

High temperatures in the mid 30s in Pittsfield, Adams, North Adams and Williamstown, mid to upper 30s in Great Barrington and Sheffield, and near 30 to low 30s over the elevated terrain and hilltowns (depending on elevation).

Easterly winds at 15-25 mph in the morning shifting to northeasterly and diminishing to 10-20 mph during the afternoon.