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Berkshire County Forecast-Friday, December 28

Posted by: | December 28, 2012 | No Comment |

The following are some snowfall totals reported to the NWS office in Albany from the recent storm:

North County: The big “winner” for the county was Savoy at 20.2″; Adams – 12″; Chesire – 12″; and Williamstown – 8″

Central Berkshire: Windsor – 13.4″; Washington – 12″; Stockbridge – 12″; Hinsdale – 10″; Becket – 10″; Pittsfield  – 9″; Lanesboro – 7.5″; Hancock – 4.5″

South County: Otis – 11.5″; Alford – 5.5″

There were a few “mesoscale” (on a scale smaller than the storm itself) phenomena which had a large impact (predominantly diminishing) on snowfall totals for Berkshire County.

1) A “gravity wave” appeared to develop and propagate over the county as the storm intensified rapidly off the Mid-Atlantic Coast Wednesday evening. These phenomena are not uncommon when a coastal storm rapidly intensifies as it moves over the warm waters of the Gulf Stream. However, it is a forecasting dilemma because they do not always develop, and they are a complicated, somewhat poorly understood physical phenomena so they are not manifested in the computer models.

To describe these waves in the most basic form, they are vertically-oriented waves that develop due to rapid ascent in the atmosphere over the intensifying surface low. Buoyancy and gravity are the vertical restoring forces that generate a vertical “oscillation” of air in the atmosphere. Essentially, the air which is accelerating upward “bounces” up and down between two very stable layers, usually inversions (temperatures increase with height instead of decrease) in the atmosphere, 1] the tropopause (transition between the weather layer, the troposphere, and the warmer stratosphere [warmed by ozone absorbing UV light from the sun], at about 30,000 feet altitude) and 2] the lowest 5-10 K feet of the troposphere near the surface where warmer air is being forced up and over colder air near the surface to the north and northeast of the surface low. This results in a “wave” of alternating upward and downward moving air radiating out toward the north/northeast of the surface low. Where the air is going up, the precipitation is enhanced and where it is going down, the precipitation shuts down.

After an initial burst of heavy snow moving south to north across the county in the early evening (upward branch of the gravity wave) the precipitation completely shut down for several hours over the county (downward branch). This is typical of a gravity wave since, apparently, it takes a while to regenerate enough upward motion to redevelop the precipitation after it shuts down from the downward branch of the gravity wave.

2) Downsloping – This occurred as very strong easterly winds forced air up (upward motion=cooling, condensation and heavy precipitation) the eastern highlands and then down (downward motion=warming, evaporation and lighter precipitation) the western slopes into the valleys. This is the reason that elevated terrain in eastern parts of the county (Savoy, Washington, Windsor, Otis, Becket) received much more snow than western portions of the county (Pittsfield, Alford, Williamstown, Hancock).

3) Mixed precipitation – There was a mixing with and brief changeover to sleet and freezing rain in the early morning on Thursday in South County and parts of Central Berkshire.

Summary: We are still along the eastern side of the trough in the jet stream wave pattern, which puts us in the path of the next developing surface low pressure system presently located over Louisiana. However, unlike the last storm, the jet stream wave pattern is more zonally (east-west) oriented so the surface low will not intensify as much and will move through much faster than the last storm, tracking off to our south off the Mid-Atlantic Coast and out to sea Saturday afternoon and evening.

Air is cold at all levels of the atmosphere so this should be an all snow event without concern for any ice or mixed precipitation. Most of the county should receive in the 2-4″ range with some spots in the elevated terrain receiving as much as 5 or 6″. The snow should begin around noon or early afternoon on Saturday. The snow should be generally light but it could be occasionally moderate and continue through the afternoon and evening. The snow will begin to taper off in the later evening but snow showers will likely continue off and on into Sunday morning.

It will become blustery and cold on Sunday with some partial clearing in the afternoon after some morning cloudiness and flurries. Temperatures will remain below normal for the rest of the week as the jet stream shifts to our south. There may be some snow flurries and showers as a cold front moves through on Wednesday, opening the door for a very cold Continental Arctic air mass (our first of the season) to move in for late week with low temperatures near zero and highs not making it out of the teens.

Friday Night

Partly to mostly cloudy and seasonably cold.

Low temperatures in the mid teens in most locations with some low teens over the elevated terrain.

Northwest winds at 5-10 mph, becoming light and then calm after midnight.

Saturday

Becoming overcast early with snow developing around noon or early afternoon. The snow will be generally light but there could be a few bursts of moderate snow. Probability of precipitation 90%. 1-3″ snowfall accumulations are likely by dark.

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

Winds light and variable in the morning, becoming east-northeasterly at 5-10 mph in the afternoon.

Saturday Night

Overcast with intermittent light snow during the evening, tapering to snow showers near midnight. Scattered snow showers should continue off and on into Sunday morning. Probability of precipitation 80%. An additional 1-2″ of snowfall accumulation is likely. Total accumulations will be in the 2-4″ range for most locations, with 5 or 6″ in some spots in the elevated terrain and hilltowns.

Low temperatures near 20 with mid to upper teens over the elevated terrain.

Winds shifting to northwesterly during the evening and increasing to 10-15 mph after midnight.

Sunday

Mostly cloudy with scattered snow flurries during the morning. No accumulation, other than a light dusting in a few places is expected. It will become partly sunny in the afternoon but will be blustery and cold.

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

Northwest winds will increase to 10-20 mph by afternoon and as high as 25 mph over the higher terrain. Gusts from 30 mph in the lower elevations to as high as 40 mph over the higher terrain.

under: Berkshire County Forecasts

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