Wisp Resort / McHenry

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McHenry, MD

Forecast Discussion

Summary

SYNOPSIS

... Lingering rain may mix with snow before ending Monday with a crossing cold front. Otherwise; generally dry and colder conditions are expected expected Tuesday through the upcoming week, with minimal precipitation chances mainly south of Pittsburgh.

NEAR TERM /UNTIL 6 AM THIS MORNING/... Areas of light rain/drizzle continue along a cold front across SW PA to SE OH. This front is expected to slow its southward progress and stall overnight, as a weak surface wave begins to approach from the west. 00Z RAOBs and model soundings indicate enough no saturation in the dendritic growth layer, and a slight chance of some very light freezing drizzle remains possible north of Pittsburgh. Impacts on roads are not expected with sfc temps above freezing, though some elevated surfaces could see a very light glaze of ice should this freezing drizzle occur. The dendritic growth region should become saturated again by morning, ending the freezing drizzle potential.

Otherwise, the potential for light rain/drizzle will continue overnight with low level moisture in place.

SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY NIGHT/... Lack of moisture in the dendritic growth zone may result in a slight chance of very light freezing rain or freezing drizzle for northern zones Monday morning. However; with a warm antecedent ground conditions, ice accumulation potential remains minimal and should be confined to elevated surfaces.

With that area of frontogenesis still draped across the region Monday, high resolution guidance indicates a weak surface wave will move along the front during the afternoon, coincident with positive vorticity advection aloft. While areas of ongoing light rain (and light snow north of Pittsburgh) will continue through the morning, this crossing surface wave and vorticity advection should result in an increase in precipitation coverage during the afternoon, especially from areas near PIT and southeast. The cold front is then progged to make a more rapid advancement to the south through the afternoon, resulting in the rain/snow transition line moving south toward the I-70 corridor

Any remaining precipitation should diminish Monday night after changing to all snow, and as the front exits to the SE. A southern stream shortwave is progged to cross the SE CONUS late Monday night through Tuesday evening. Areas mainly south of I- 70 could see a chance of light snow as an inverted surface trough extends nwd across the Appalachians. Elsewhere, dry weather is expected as surface high pressure builds in across the Great Lakes region.

Much colder temperature is expected after the front clears the area, with readings 5 to 10 degrees below average.

LONG TERM /WEDNESDAY THROUGH SUNDAY/... Recent 12Z long range guidance seems to better align, suggesting a digging west coast trough of low pressure should result in a noticeable pattern shift during the extended period. Height rises ahead of that trough across central CONUS, combined with existing low pressure centered near Hudson Bay, should situate the area within northwesterly flow aloft and translate to much colder conditions on the order of 5 to 10 degrees below average.

Regarding precipitation; southern stream low is progged to remain suppressed to our south Wednesday, with surface high pressure in place across the Upper Ohio Valley region. Another southern surface low could result in slight/low chance POPs for areas S of the WV/PA border Wednesday night Wednesday night through Thursday night, with dry weather expected elsewhere under a surface ridge of high pressure.

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