Summary: Yesterday’s weather event in Berkshire County was highly elevation dependent, with the elevated terrain/hilltowns getting significant accumulations of heavy, wet snow and the lower elevations/valley locations getting mostly rain after some wet snowfall overnight into the early morning hours. Snowfall totals reported to the National Weather Service in Albany were generally in the 1-3″ range in the lower elevations, with 1″ at Sheffield, 1.2″ in Pittsfield, 1.8″ in Lenox, and 2.5″ in Williamstown. However, the hilltowns were another matter entirely, with Peru reporting 8″ and Savoy 12″. This type of elevation snowfall is typical of the transition seasons, late fall/early winter (November, early December) and late winter/early spring (usually late March into early April) as the higher sun angle raises near surface temperatures considerably during the day (even with cloud cover) so that even though temperatures are cold enough aloft for snowfall, temperatures in the valleys climb well up into the 30s so that the snow changes to rain. It is interesting that we had this event in late February this year and as I look toward the pattern for next week I am reminded that the length of our winter season has been decreasing in recent years (global warming) and late February/early March may be becoming the new mid/late March. In fact, it has been noted by satellite observations that the “greening line” has advanced 2 weeks farther north in the Spring since the 1980s.

As the cold pool aloft (aka upper-level low) that was responsible for generating our “storm” yesterday drifts eastward over us today, it continues to moderate and weaken as it becomes “elongated/stretched-out” zonally (west to east). However, it will drift very slowly offshore over the next few days and weak disturbances rotating around it should keep us under considerable cloud cover (although there will be some sunny breaks…yay high sun-angle) and even give us a few periods of light snow showers (mixed with rain in the lower elevations during the day on Friday). Our temperatures will also stay relatively cool, as we will be under the eastern portion of a large-scale trough (southward dip) in the jet stream which is covering the eastern half of the country. It will take many days for this relatively cool, cloudy weather to clear as the trough slowly, slowly begins to lift out. However, I am seeing indications that a warm ridge in the jet stream will develop in the center of the U.S. mid-week next week and attempt to move east over our region, with an associated surface high pressure system by late week. If this occurs, we could be in for an early taste of spring by late week/early next weekend. Right now it looks like temperatures could reach the 50s with sunny skies, not 60s or 70s but, hey, it is early March and beggars can’t be choosers. Let’s hope that the long-range models are correct. One note, the models are also hinting that the trough will try to deal us a parting blow by developing a coastal low around Wednesday. However, right now it appears that it is likely to pass well to our south and out to sea.

Thursday Night

Mostly cloudy with a good chance of a snow shower, predominantly before midnight. Probability of precipitation 50%. There may be a dusting in a few locations, mostly over the elevated terrain.

A persistent cloud cover will prevent much radiational cooling so temperatures will not fall too much overnight. Low temperatures in the upper 20s to near 30 in most locations, mid to upper 20s over the elevated terrain.

Northwest winds at 5-10 mph.

Friday

Mostly cloudy in the morning. The cloud cover will likely break up for a time near midday (late morning to early afternoon), becoming partly sunny (50-75% cloud cover), particularly over South County. However, this will destabilize the atmosphere somewhat so there is the chance of a few scattered snow showers or flurries developing, particularly over the Taconics (rain shower or sprinkle in the lower elevations), as it becomes mostly cloudy again mid to late afternoon. Probability of precipitation 30%. No accumulation expected.

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.

It will be a bit breezy with northwest winds at 10-15 mph.

Friday Night

Remaining mostly cloudy. There is still the chance of a snow shower or flurry. Probability of precipitation 40%. The greatest likelihood is, once again over the Taconics (upslope region with a northwest flow). There may be a dusting in a few locations over the elevated terrain.

Temperatures will be a little lower than Thursday night as slightly colder air moves in. Low temperatures in the mid to upper 20s in most locations with some low 20s over the elevated terrain.

Northwest wind at 5-10 mph.

Saturday

Mostly cloudy to overcast and slightly colder with a good chance of snow showers or flurries, particularly in central and northern Berkshire. Probability of precipitation 50%. A coating of snow is possible in some locations with up to a half inch in a few spots over the higher elevations.

High temperatures in the mid 30s in most locations, some upper 30s in the lower elevations of South County and low 30s over the elevated terrain.

Northwest winds at 5-15 mph.

Summary: Precipitation should be all snow overnight and there may be some significant accumulations by morning. During the day on Wednesday, the precipitation will continue to fall moderate at times into the afternoon. Temperatures look to remain very close to freezing from the ground up to about 10,000 feet so precipitation type during the day is somewhat uncertain. However, a significant change with yesterdays forecast is that I think that it will be a little warmer at the surface. Therefore, there is less risk for freezing rain or icing, even over the elevated terrain and this now looks predominantly like a snow and rain event. At this time of year, this is likely to be an “elevation” event with significant differences in snow accumulation depending on your elevation.

The snow that falls overnight tonight should be “wet” snow with temperatures close to freezing. Therefore, the snow will tend to melt when it hits the road, particularly if the roads are treated. Still, snow will fall moderate to heavy at times after midnight into the early morning, permitting snow to accumulate on the roads faster than it can melt, causing snow-covered or slush-covered roads at times, right into the morning “rush” hour. When it is not snowing heavily overnight, the roads may just be wet in the lower elevations but still probably snow covered over the elevated terrain. During the day, wether it is snowing or raining, the rising temperatures near the surface and the high sun-angle should turn the roads wet over the course of the day.

The time line for this precipitation event looks like this:

Snow should develop from south to north across the county, beginning near midnight, possibly an hour or two before midnight. Snow should fall fairly steadily after midnight, moderate to even heavy at times til morning. The snow may mix with and begin to change to rain in the lower elevations of South County by 6 or 7 am. Likely total snowfall accumulations by morning 3-6″ with the lower amounts most likely in the lower elevations to the north and the higher amounts most likely in the higher elevations in central and southern portions of the county. During the morning hours, wet snow will likely mix with and change to rain between 7 and 10 am in the lower elevations. It is likely to take longer to transition to rain in the elevated terrain where it may stay wet snow until noon in northern areas. There is still a chance that it could remain wet snow for the entire event over the elevated terrain in central and northern Berkshire. Daytime snow accumulations are difficult to predict due to the uncertainty and timing of the changeover to rain. However, in the lower elevations, snow accumulations are unlikely to total more than an additional coating to an inch or so during the morning given the rising temperatures and sun-angle. However, additional snowfall totals during the day in the elevated terrain could range between 1-4″ depending on elevation and when or if the snow changes over (highest totals will most likely be in the north-e.g. Savoy, Florida). Keep in mind that the accumulations during the day are likely to be mostly on grassy surfaces. Also, even though if you total the amounts I have predicted you would come up with as much as 10″ over the elevated terrain, there will not be that much on the ground. Snowfall totals are compiled each hour and there will be considerable melting going on as the snow falls during the day.

Precipitation will begin to taper off during the mid to late afternoon. Any precipitation will change back to all snow during Wednesday evening. However, there should be nothing more than a little light snow or snow showers overnight Wednesday with nothing more than an additional inch or so of accumulation. The should be some snow showers on Thursday as well as the upper-level cold pool moves over the region and destabilizes the atmosphere. Once again, not much accumulation is expected.

Tuesday Night

Overcast with snow developing from south to north between 10 pm and midnight. Snow moderate to even heavy at times after midnight. Probability of precipitation 100%. Most likely snowfall accumulations 3-6″. The snow may begin to mix with or change to rain in the lower elevations in South County toward daybreak.

Low temperatures near 30 to the low 30s in most locations with high 20s over the elevated terrain.

Easterly winds at 5-10 mph in the evening, increasing overnight to 15-25 mph by morning. There will likely be gusts over 30 mph, particularly over the elevated terrain.

Wednesday

Wet snow early, mixing with and changing to rain in the lower elevations during the morning (~7-10am), later (late morning-noon, if at all) over the elevated terrain. Probability of precipitation 100%. Likely additional snowfall accumulation a coating-1″ over the lower elevations, 1-4″ over the elevated terrain

High temperatures in the mid to upper 30s in Pittsfield, Adams, North Adams and Williamstown, near 40 in Great Barrington and Sheffield, and low to mid 30s in the elevated terrain and hilltowns.

Easterly winds at 15-25 mph, diminishing during the afternoon, dropping to 5-10 mph by evening.

Wednesday Night

Overcast with occasional rain or snow showers in the evening, scattered snow showers after midnight. Probability of precipitation 60%. Most likely snowfall accumulation 1″ or less.

Low temperatures in the low 30s in most locations, near 30 over the elevated terrain.

Light east-southeasterly winds.

Thursday

Overcast with scattered snow showers, particularly during the afternoon. Snow may be mixed with rain in the lower elevations. Probability of precipitation 60%. Most likely snowfall accumulations 1″ or less.

High temperatures in the mid to upper 30s in Pittsfield, Adams, North Adams and Williamstown, near 40 in Great Barrington and Sheffield, and low to mid 30s in the elevated terrain and hilltowns.

Light east-southeasterly winds in the morning shifting to northwesterly at 5-10 mph in the afternoon.

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.

I do not see anything today that would warrant much of a change to the forecast I made yesterday…

Any precipitation we get tonight and tomorrow should remain light. In addition, temperatures are above freezing in all of the larger towns (lower elevations) ranging between 33 and 36 degrees and should hold fairly steady through the night and then rise a few degrees more degrees during the day tomorrow. Therefore, any snow that does fall will have a difficult time accumulating. Over the elevated terrain temperatures are a little colder, ranging between 29 and 33 degrees, with the 29 being recorded at 1900 feet in Peru. Most of the temperatures available from the elevated terrain are 31 or 32. As a result, there is a better chance of some accumulation over elevated terrain, predominantly at the higher elevations.

From late afternoon today til about midnight scattered light mixed precipitation is likely around the county. After midnight and through tomorrow any precipitation should change to all snow. A period of light snow may develop across the county after midnight into Sunday morning. There should be a pause in any steady light snow, with only some scattered snow showers possible, mid-morning til late afternoon Sunday. I actually think our best chance for accumulating snow from this coastal low will be late afternoon into evening on Sunday as some moisture “wrapping around” the departing surface low from off the ocean moves south out of Vermont.

Most likely total accumulations by the time the precipitation ends Sunday Night:

Lower elevations in the western portions of the county, including all of the large towns….no accumulation – 1″ in South County, a coating – 2″ in central and northern Berkshire.

Elevated terrain and hilltowns….. a coating to 2 or 3″, with the highest amounts in the higher elevations in central and northern Berkshire.

I think that there will be virtually no accumulation before midnight and only a coating to 1″ at most by Sunday morning with the best chance for accumulations (still only and inch or two at most) occurring late Sunday afternoon into Sunday evening.

I still believe that the lower ends of the ranges of these accumulation estimates are more likely than the higher ends…i.e. NOT MUCH!

Summary: The dynamics associated with this weekend’s “storm” (and I use the term loosely) are looking even less impressive today. The upper-level disturbance looks weaker, with less perturbation of the jet stream. This should result in less upward motion in the atmosphere and a weaker surface low pressure system. In addition, with a “flatter” (less amplified) jet stream, the surface low forming off the coast in response to the upper-level disturbance will form farther south and east and progress fairly quickly eastward. Bottom line: if you are a snow lover, this will be a BUST. In fact, with this scenario I would not be surprised if we receive no accumulating snowfall at all in Berkshire County.  In addition, as mentioned yesterday, above freezing air will likely also move in aloft, turning any snow to sleet and even freezing rain or rain for a time Saturday evening in South County and, possibly, in central and northern Berkshire as well.

The timeline for this event looks something like this: Only some scattered snow flurries or snow showers into tomorrow afternoon. If any steady light snow develops mid to late in the afternoon it will likely not accumulate with temperatures at or slightly above freezing and a high sun-angle this late in the winter. During the evening hours until sometime near or after midnight there will likely be scattered light precipitation across the County. South County will most likely see light sleet and/or freezing rain or rain with the rest of the county seeing mostly snow with some mixing of sleet and freezing rain possible. I do not expect any signigicant icing as the precipitation should be light and temperatures will be close to freezing. There is a chance that a steadier period of precipitation could develop during this period and give some accumulating snow. As the storm passes well to our east after midnight and toward Sunday morning, any steady precipitation should come to an end. We may receive some snow showers on Sunday due to moisture wrapping around the low and being lifted by the terrain. However, temperatures will be above freezing in most locations and I believe that this will result in nothing more than a dusting in the elevated terrain.

My best estimates for snow accumulation are:

Nothing (zero) to 1-2″ in the lower elevations in the western portions of the county, including all of the large towns. The lowest amounts should be in South County where all snow is less likely and “wintry mix” or rain is more likely. An inch or two of wet snow may fall to the north in Williamstown, Adams and North Adams although I would not be surprised if all of these areas had no accumulation or only a coating. In the elevated terrain to the east 1-3″ could fall, with the highest amounts most likely over the highest terrain in the far eastern regions (e.g. Savoy, Peru). Once again, even these areas may get no accumulation or only a coating.

My gut feeling about this storm is that we will not get much of anything, even though the computer models are still “spitting out” more than measurable amounts of precipitation. If I was making decisions for myself [caveat :-)]I would not cancel any plans because of this “storm”.

Friday Night

Overcast with a chance of a snow flurry or light snow shower toward morning. Probability of precipitation 30%. No accumulation expected.

With overcast skies, temperatures will not drop much, and low temperatures will be in the upper 20s in most locations with some mid 20s over the elevated terrain.

Light southeasterly winds increasing to 5-10 mph by morning.

Saturday

Overcast with the chance of a snow flurry or snow shower in the morning. It is possible that a period of steadier light snow or mixed precipitation could develop mid to late afternoon. Probability of precipitation 60%. Accumulations most likely nothing to a coating, although as much as 1/2″ is possible over the elevated terrain.

High temperatures in the low to mid 30s in most locations and near 30 to low 30s over the elevated terrain and hilltowns.

Southeast winds at 5-10 mph, becoming easterly late.

Saturday Night

Overcast with intermittent light precipitation. During the evening into the early morning hours a mixture of frozen precipitation types or even rain is most likely in South County with increasing chances of all snow as one moves north within the county. The best chance for all snow is the northeastern elevated terrain. Towards daybreak any precipitation will likely turn to all snow throughout the county. The best chance for steady precipitation is before midnight. Any precipitation should diminish after midnight and end by morning. Probability of precipitation 80%. Any snow accumulation should be light (see summary above). The greatest chance of accumulation (3″ at the most) will be over the elevated terrain to the east.

Temperatures will hold fairly close to freezing in the lower elevations in south and central portions of the county past midnight and then drop into the upper 20s to near 30 by morning. Temperatures will likely be in the upper 20s to near 30 to the north and in the elevated terrain past midnight and then drop into the mid to upper 20s by morning.

Easterly winds at 5-10 mph becoming light northerly by morning.

Sunday

Mostly cloudy in the morning. It may become partly sunny at times in the afternoon, particularly in South County. There is still a good chance of a few snow showers. Probability of precipitation 50%. Nothing more than a coating, mostly in the elevated terrain, is expected. An area of steadier light “wrap around” snow or snow showers may move from north to south into the county from Vermont later in the afternoon and into the evening.

High temperatures in the mid to upper 30s in Pittsfield, Adams, North Adams and Williamstown, near 40 in Great Barrington and Sheffield, and low to mid 30s over the elevated terrain and hilltowns.

Light northwest winds in the morning, increasing to 8-12 mph in the afternoon.

Summary: The computer models have begun to diverge on their solutions to this weekend’s storm. Just on the basis of precipitation totals being generated by the models, we could get anywhere from a few inches of snow (European-ECMWF) to 6-12″ (American-GFS) to 2 feet (American-NAM). However, you are counting on me to use my experience and knowledge of the atmosphere to try to sort this out (since mathematical models can’t “think”…theoretically). So here goes…..

I think that my suspicion yesterday (see CAVEAT) that the set-up in the atmosphere for a big snowstorm did not look right will probably be correct. To begin with, I do not think the NAM model solution looks realistic so, for now, I am going to disregard it and concentrate on the two models which look more realistic and tend to be more reliable with winter coastal storms (ECMWF and GFS). The disturbance in the jet stream which will be responsible for generating the surface low pressure system along the coast looks to be weaker than it did yesterday. Upward motion and the surface low should be relatively weak which should limit precipitation rates somewhat. It will also take a while for the storm to get going so that by the time it “intensifies” much of the precipitation will be to our south and east. In addition, in part because of the weakness of the coastal low, above freezing air will likely sneak in aloft (about 5000 feet up) for a time Saturday evening and turn the snow to sleet. This will almost certainly happen in South County, possibly in central Berkshire as well. This will limit snowfall totals further. Also, temperatures at the surface will be close to freezing so the snow should be fairly “wet”, limiting accumulation as well.

The timeline looks like this: Steady precipitation should not begin until Saturday evening. There may be some widely scattered snow showers during the day on Saturday, but nothing more than that. Steady snow should begin sometime Saturday evening and continue into Sunday morning. The snow will vary in intensity, mostly light to moderate. Snow will likely change to sleet in South County during the evening, and stay sleet til well past midnight. It may change to sleet for a time in central Berkshire as well. It will likely stay all snow in North County. By the time the “storm” ends on Sunday I think the most likely snowfall totals will be as follows: South County 1-4″, central Berkshire 3-6″, North County 4-7″. Expect the higher totals in these ranges to be over the elevated terrain and where/if there is less sleet. These estimations are somewhat of a guess at this point since the “storm” is somewhat complex and fluid and still 2-3 days off. I will continue to update this forecast…..

Before this mess arrives we should have a fairly tranquil end to the work week as surface high pressure builds in, briefly, on Friday. However, clouds will begin to build in during the afternoon and overnight.

Thursday Night

Partly cloudy this evening, becoming mostly clear after midnight. Winds will diminish (finally) and it will be quite cold.

Low temperatures in the low teens in most locations, upper single digits over the elevated terrain.

Northwest winds at 10-15 mph in the evening will diminish overnight, becoming light northerly toward morning.

Friday

Mostly sunny, with only some high, thin clouds in the morning. Increasing clouds during the afternoon. Much milder than previous days.

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

Winds light and variable.

Friday Night

Mostly cloudy to overcast, with only the slight chance of a snow shower or flurry.

Temperatures will not drop much with the cloud cover. Low temperatures in the mid to upper 20s in most locations.

Light southeast wind in the evening, increasing to 8-12 mph by morning.

Saturday

Overcast with the chance of a snow shower through mid afternoon. Light snow or, possibly sleet in South County, is likely to develop sometime late afternoon or, more likely, in the early evening. Little if any accumulation expected by dark.

High temperatures in the mid to upper 30s in most locations with some low 30s over the elevated terrain.

East-southeast wind at 10-15 mph.

The short-term forecast for Berkshire County (next few days) has not changed since yesterday [cold, breezy, mostly cloudy and scattered lake-effect snow showers through tomorrow] and so I will not submit a “full” forecast until tomorrow. However, the scenario is beginning to look much more interesting for this weekend so I would like to discuss that. As I mentioned in yesterday’s forecast, a trough in the jet stream wave pattern moving out from over the Rocky Mountains is generating a surface low pressure system over the Great Plains that will result in heavy snow for Kansas, Nebraska and Iowa tonight and tomorrow. The trough is not particularly deep (the jet stream wave pattern is fairly zonally (west-east) oriented [not particularly amplified]) and so the dynamics are not particularly strong with this storm. Therefore, the surface low will be fairly weak and winds will be relatively light and the air is not particularly cold so this will not be a classic Great Plains “blizzard” with very strong winds, reduced visibility and frigid temperatures that is typical of this region with featureless terrain and access to arctic air from Canada. However, as is becoming fairly typical for this winter, snowfall totals will be very heavy (over one foot) because of large amounts of moisture (water vapor) in the atmosphere associated with this storm [global warming?].

As the trough propagates eastward, it will “flatten out” even more, and the surface low will weaken rapidly and, essentially, dissipate as it moves into the Great Lakes Friday and Saturday. However, an upper-level disturbance (counterclockwise rotating cold pool aloft associated with a jet “streak” [short burst of particularly strong jet stream winds] will rotate through the base of what remains of the trough as it approaches the East Coast on Saturday. Yesterday it appeared that this disturbance was not as strong as it looks in all of the computer model runs today and I was skeptical that we could get much in the way of a snow storm this weekend. However, it now looks like, even though the jet stream pattern will remain un-amplified (NOT a typical scenario for a big East Coast snowstorm) the strong disturbance will create a sharp “kink” in the trough as it moves over the coast on Saturday. This, if it occurs, will create large amounts of divergence in the jet stream winds that will essentially “suck” air out of the atmospheric column below it. This will create strong upward motion (rising, cooling and condensing air) which likely will result in an area of heavy precipitation and surface low pressure off the Mid-Atlantic Coast. In addition, as with the last snowstorm, as the cold pool aloft moves over the warm Gulf Stream the upward motion will increase (due to environmental instability) and this may enhance the upward motion further. On top of this, there will be plenty of moisture available for evaporation from the Gulf Stream as the storm gets going.

The configuration and dynamics of this storm do not appear as prodigious as the one that crushed southeastern New England earlier so I do not see there being nearly as much snow with this storm. However, the storm looks to track closer to the coast and Berkshire County may get as much as with that storm. However, we will be close to the snow/rain line with this storm (although it looks like all snow for us right now) so with temperatures near freezing the snow will be “wetter” which should hold down accumulations.

Bottom line: Snow developing sometime Saturday afternoon or evening and continuing, heavy at times, into Sunday. Most likely accumulation, right now, looks like about one foot. CAVEAT: I do not feel this is a high confidence forecast at this time. This is not the classic appearance of a big snowstorm for Berkshire County, even though the models seem to be converging on this result. This scenario will likely change over the next few days so I will continue to update each day…..

Summary: As I write this (2:00) the precipitation shield associated with the advancing cold front is just to our west. From surface reports I am seeing I think we are going to get pretty much all wet snow, even at lower elevations (the larger towns). Temperatures are in the low 40s in the lower elevations but dew points are in the low 20s so I think any rain that falls at the onset will turn rapidly to wet snow as temperatures drop into the low to mid 30s. It should be all snow in the elevated terrain and hilltowns where temperatures are, even now, in the low to mid 30s. There will be a period of snow that should be fairly steady (although it will vary in intensity) for several hours and then end by 8 pm or so with another brief band of snow showers following behind by a few hours (around 10 or 11 pm). I do not think the accumulation outlook is much different than yesterday. Most places in the lower elevations should get around 1″ with closer to 2″ in the elevated terrain where a few spots may receive as much as 3″. Even though temperatures will be near freezing, the roads may become snow or slush covered after nightfall, particularly on the secondary roads over the elevated terrain.

After our brief respite today, winter will again return to Berkshire County as the cold front passage opens the door to 2 days of cloudy, windy and cold conditions with occasional bouts of scattered lake-effect snow showers. The weather will moderate on Friday as weak surface high pressure temporarily builds in with some sunshine and more seasonable temperatures.

A trough in the jet stream wave pattern moving out of the Rockies will generate a surface low pressure system that will give the Great Plains heavy snow on Thursday. This trough will flatten out and the  surface low will subsequently die as it moves east through the Great Lakes. What remains of the trough (low amplitude) will probably generate a weak coastal low off the Mid-Atlantic coast Saturday night and Sunday. We may get a little snow (possibly none) from this system but it certainly doesn’t look like anything plowable right now.

Tuesday Night

The period of wet snow which begins this afternoon should end by 8 pm or so, followed by another brief period of snow showers a few hours later. Skies will remain mostly cloudy after midnight with a few scattered lake-effect snow showers in central and northern Berkshire with partial clearing in South County. Probability of precipitation near 100%. Snowfall accumulations around 1″ in the lower elevations, 2″ with as much as 3″ more likely over the elevated terrain.

Temperatures will remain near freezing until around midnight and then fall fairly quickly after midnight. Low temperatures should reach near 20 in most locations by morning, mid to upper teens over the elevated terrain and hilltowns.

Southwest winds at 5-10 mph in the evening will shift to west-northwest after midnight and increase to 10-20 mph.

Wednesday

Mostly cloudy, quite breezy and cold. Intermittent lake-effect snow showers are likely, particularly over central and northern Berkshire, particularly in upslope regions (west and northwest facing terrain). Probability of precipitation 60%, 40% in South County. There will likely be a dusting of snow in some locations with up to 1″ in a few spots over the higher terrain.

High temperatures in the low to mid 20s in Pittsfield, Adams, North Adams and Williamstown, mid 20s in Great Barrington and Sheffield, and upper teens to near 20 over the elevated terrain and hilltowns. Wind chill temperatures occasionally dropping to the single digits to low teens.

West-northwest winds at 10-20 mph (wind speed increasing with elevation) with occasional gusts over 30 mph.

Wednesday Night

Remaining mostly cloudy, breezy and cold with a chance of a lake-effect snow shower or flurry in the evening. Probability of precipitation 30%. Nothing more than a dusting.

Low temperatures in the low teens in most locations, upper single digits over the elevated terrain. Wind chill temperatures will occasionally drop to 0 to -10.

West-northwest winds will continue to blow at 10-20 mph (wind speed increasing with elevation) with occaisional gusts over 30 mph.

Thursday

Remaining mostly cloudy, breezy and cold. There may be some partial clearing in the afternoon, particularly in South County. There is still the chance of a few scattered lake-effect snow showers or flurries. Probability of precipitation 30%.

High temperatures in the low to mid 20s in Pittsfield, Adams, North Adams and Williamstown, mid to upper 20s in Great Barrington and Sheffield, and upper teens to low 20s over the elevated terrain and hilltowns (depending on elevation). Wind chill as low as the upper single digits to lower teens.

Northwest winds at 10-20 mph (wind speed increasing with elevation) with occaisional gusts over 30 mph.

The forecast has not changed much since yesterday. I expect it to be mostly sunny and turning mild in the morning tomorrow with increasing clouds through mid-afternoon. Temperatures will approach 40 in many locations. Fairly steady precipitation should begin sometime between 3 and 5 pm and end around 8 or 9 pm. My take on precipitation type or snow accumulation has not changed since yesterday. Temperatures will be in the mid to upper 30s when the precipitation starts but will drop quickly once it begins. It may start as a brief period of rain or mixed rain or snow over the elevated terrain and hilltowns but should turn rapidly to all snow. I think it more likely that it will be snow for the duration in those locations. In the lower elevations, the rain or mix will likely last longer, as much as an hour, before it turns to all snow. Temperatures should remain at freezing or just above freezing in all locations for most of the event so the roads should remain mostly wet, with accumulations predominantly on grassy surfaces, although there will likely eventually be some snow cover on the secondary roads in the elevated terrain. I think the most likely accumulations would be a coating to 1″ in the lower elevations and 1-2″ in the elevated terrain and hilltowns with a few spots getting as much as 3″ (can you say “Peru”). After the cold front moves by, and the steady snow ends, some scattered lake effect snow showers will likely develop overnight without any additional accumulation other than a dusting. It will turn colder and breezy on Wednesday with mostly cloudy skies and scattered lake-effect snow showers, mostly in central and northern Berkshire. However, it will not be as windy or frigid as the conditions we experienced the past few days. Temperatures will remain in the 20s on Wednesday and then drop into the single digits Wednesday night. Temperatures should become more seasonable by Friday. It is beginning to look like there is a fairly strong likelihood that we could get some snow over the weekend. I will update this tomorrow….

Summary: As the coastal storm deepens rapidly (central pressure of 965 mb!) and departs for the Canadian Maritime this afternoon, the pressure gradient between the intensifying surface low and approaching surface high pressure from southern Canada and the Great Lakes has also intensified. As a result, west-northwest winds have become strong and gusty (39 mph gust at the BCC weather station). The winds are driving very cold air for this late in the winter quite far south as the trough in the jet stream pattern has dipped all the way to the southeastern states. Temperatures dropped into the mid 20s in northern Florida this morning and are only in the 50s throughout Florida (even Miami) this afternoon.

As the trough becomes centered over us tonight, it will become quite frigid, despite the strong winds. If winds were calm, temperatures would drop well below zero tonight. As it is, with temperatures in the single digits and winds of 15-25 mph, wind chill temperatures will drop to -10 to -20 at times so if you have to go out, watch for exposed skin. On Monday, there will be plentiful sunshine but there will still be a gusty wind so it will still feel quite cold.

Monday night through Tuesday evening, the deep trough in the jet stream pattern will final lift out and a weak ridge will briefly build in. This will be followed by another trough which will not be quite as deep and so, even though it will turn colder for mid-week it will not be as frigid as our present conditions. As this next trough approaches, it is generating a surface low pressure system along its eastern edge (surface low pressure [storms]in middle latitudes are almost always in this location in the jet stream wave pattern). This low pressure system will track through the Great Lakes and drag its warm front across our region Monday night followed by its cold front Tuesday afternoon and evening. The warm front will likely come through dry, with nothing more than some cloudiness.

It will then get milder on Tuesday as we move into the “warm sector” of the Great Lakes storm system and aside from some thin mid and high-level clouds we will see a fair amount of sunshine through early afternoon. Temperatures will likely reach 40 degrees in the lower elevations and the mid to upper 30s in the elevated terrain. The cold front will move through from late afternoon into the evening with a fairly solid band of precipitation. Precipitation type is a bit of a tough call right now. It will be cold enough aloft to support snowfall. Therefore, I think that even though it may start as a little rain or mixed rain and snow in the elevated terrain and hilltowns, those areas will receive predominantly snowfall with 1-3″ of wet snow accumulating. In the lower elevations (all of the large towns and “cities”) it will be too warm at low-levels to support snow initially so rain or mixed rain and snow will likely fall for an hour or two before it turns to all snow. In these locations only a dusting to 1″ of wet snow will likely fall.

Sunday Night

Partly cloudy this evening, becoming clear after midnight, windy and very cold.

Temperatures will fall into the low to mid single digits in most locations, near zero over the elevated terrain. Wind chill temperatures as low as -10 to -20 at times.

West-northwest winds at 15-30 mph, with the strongest winds within this range over the elevated terrain, with occasional gusts over 40 mph.

Monday

Abundant sunshine but still windy and cold.

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

West-northwest winds at 15-25 mph through early afternoon, with occasional gusts to 35 mph, diminishing somewhat later in the afternoon.

Monday Night

Except for a period of cloudiness as the warm front passes through near midnight, it will be mostly clear.

It will not be nearly as cold as Sunday night. Low temperatures will occur before midnight and will likely be in the mid to upper teens in most locations, with some low teens over the elevated terrain. Temperatures will begin to rise after midnight (warm frontal passage) and reach the low to mid 20s by morning.

West-northwest winds at 5-10 mph in the evening, becoming light and shifting to south-southwesterly near midnight. Southerly winds after midnight will increase to 8-12 mph by morning.

Tuesday

Mostly sunny early, then increasing mid and high-level clouds from mid-morning through early afternoon. Becoming overcast with a period of precipitation between mid-afternoon and early evening. As discussed in the summary, this will be mostly wet snow in the elevated terrain and hilltowns although it may start as a little rain or rain and snow mixed. The rain or rain/snow mixture will last longer in the lower elevations (possibly an hour or two) before it changes to wet snow. Probability of precipitation 80%. Most likely snowfall accumulations a dusting to 1″ in the lower elevations with 1-3″ in the elevated terrain and hilltowns.

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

South-southeasterly winds at 10-15 mph.