Wisp Resort / McHenry

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McHenry, MD

Forecast Discussion

Summary

SYNOPSIS

... Snow showers will decrease in coverage and intensity this evening, with record cold possible Wednesday morning. Building high pressure will provide dry weather for the rest of the week, with continued below normal temperatures.

NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Lake-enhanced NW flow snow showers continue to stream across the region. The best coverage continues to be seen north of I-70 and along west-facing slopes. The axis of the heaviest snow showers has started to creep to the northeast, away from our office here in Moon. This trend should continue as the 500mb trough axis swings east and surface ridging starts to build from the west. However, lingering steep lapse rates and inversion heights of around 8000 feet will continue to support brief moderate to heavy snow showers. Both of these parameters will become less favorable with time through the evening. So, considering all of the above, snow shower coverage and intensity will begin to wane over the next few hours. Looking at another possible 1-2 inches generally northeast of Pittsburgh centered around US-422, with perhaps a bit more in the Winter Weather Advisory area across NW PA with better lake enhancement. Another inch is likely along the ridges, with generally less than an inch elsewhere. Planning on allowing the current Winter Weather Advisory to ride as is.

By midnight, expect snow shower coverage to be isolated and confined to areas along/north of I-80 and in the ridges, with all activity ceasing by 12Z as high pressure builds into the Middle Ohio Valley. This will allow for a clearing sky across much of the region, as well as diminishing wind. With fresh snow cover as well, have trended temperatures below most of the blended guidance. A few record low values are in jeopardy - see the Climate section below for details.

SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... Dry weather will continue through this period. The surface high will slide across the region on Wednesday. The sunnier period will be during the morning hours. By afternoon, mid-level flow goes briefly zonal, and high clouds begin to increase. 850mb warm advection commences during the afternoon, but this will likely happen too late to allow temperatures to rise above freezing for most of the CWA.

Mostly cloudy conditions will dominate Wednesday night into Thursday in deeper warm advection ahead of a shortwave crossing the MississippiValley Wednesday night. This wave will weaken and skirt the eastern Great Lakes on Thursday, keeping deeper moisture to our north, and thus precipitation from this system is still not anticipated for our forecast area. Cloud cover will then lessen Thursday night as weak high pressure builds in. Temperatures will moderate somewhat, but values will remain around 10 degrees below normal for Thursday and Thursday night.

LONG TERM /FRIDAY THROUGH MONDAY/... Below-normal temperatures will continue through Saturday under broad upper troughing across the northeast CONUS. A weak frontal boundary will try to sink into our region Friday/Friday night, but it will run into quasi-zonal flow which will impede its progress. However, a slight chance of rain/snow showers was added to areas north of I-80 for this boundary.

Thereafter, rising 500 mb heights between east coast and Great Plains troughs will lead to temperatures warming towards seasonable levels by Sunday. PoPs will finally return to the forecast early next week as that western trough rotates across the central and southern Appalachians, bringing moisture back northward.

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