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Forecast Discussion

Summary

SYNOPSIS

... High pressure will cross overhead tonight. A low pressure system will move from the southern Plains into the Ohio River Valley during Sunday night through Tuesday to provide mainly rain for the Mid Atlantic.

NEAR TERM /THROUGH SUNDAY/... As of 715 PM EST Saturday...

Skies are generally clear across the region this evening, but satellite imagery shows mid/high clouds approaching from the west/southwest. This will bring increasing clouds overnight into Sunday, though any chance for precipitation will hold off until very late in the day west of the Blue Ridge. Guidance is a bit more robust with arrival of precipitation so have increased POPs a bit in the west late Sunday into Sunday night.

Previous discussion...

Confidence is high for dry weather during tonight and tomorrow morning, but clouds will increase on Sunday afternoon.

High pressure continues to gradually build eastward over the Mid Atlantic, while the air mass has become quite dry with dewpoints mostly in the single digits. Northwest winds should subside by this evening as the pressure gradient relaxes. Clear skies and light winds overnight will allow good radiational cooling, especially across the Piedmont and in sheltered mountain valleys west of the Blue Ridge.

Sunday should be tranquil overall for most locations, but high pressure will drift toward the coast by the afternoon. Meanwhile, a low pressure system organizing over the southern Plains will begin to lift toward the northeast. Clouds will steadily increase west of the Blue Ridge by the afternoon, and moisture may reach southeast West Virginia in the evening according to the high-resolution models. The precipitation could begin as a light wintry mix of rain, sleet, and snow across the higher elevations of Greenbrier County due to the wet-bulb effect that will cool the lower layers of the atmosphere. Surface temperatures will struggle to get above freezing due to preexisting snow cover. However, this moisture will have to saturate the lingering dry air before it can reach the ground.

SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 125 PM EST Saturday...

Expect cold, rainy conditions Monday into Monday night with the potential for pockets of freezing rain at the higher elevations across the northwest and northern parts of the area.

For Sunday night, the weak feature that start to crest the top of the upper level shortwave ridge parked over our area on Sunday, will continue its progress eastward Sunday night. However, precipitation will be primarily confined the western sections as what limited moisture the feature advects into the area will struggle to head too far east as it encounters dry air. The atmosphere over the region will still be on the relatively dry side as the light precipitation arrives. The temperature/dew point structure will be such in the lower levels that there could be a quick shot of light sleet across parts of southeast West Virginia, and neighboring sections of southwest Virginia. Patchy light rain will be more common farther south into the forecast area where surface and near surface temperatures will be above freezing. By daybreak Monday, the energy associated with this feature is expected to be heading into eastern VA/NC.

The notable weather maker for this portion of the forecast will be associated with the approach and passage of a warm front. This front extend eastward from an area of low pressure that will be heading from Kansas into Missouri on Monday and then into the area of central Illinois by late Monday night. As the warm front approaches and then crosses the region on Monday, look for rain to overspread the area from southwest to northeast. The vast majority of the region will be mild enough for the precipitation to fall as a cold rain. Some of the higher ridges of southeast West Virginia, east across the Alleghanies, and then to the crest of the Blue Ridge may be cold enough for pockets of freezing rain that could last into Monday night. However, these pockets will grow smaller in number during the day Monday as temperatures slowly rise. Likewise, on Monday night, we are expecting an increasing, moist and mild southwest flow too allow for slowly rising temperatures through the night. This process will also allow for those few pockets of freezing rain to shrink in number so that by the early morning hours of Tuesday, plain rain is forecast for all area. This process will also mean the low temperature Monday night will occur right around sunset.

The rain Monday into Monday night is expected to be a generous one for this time of year. Values off the NAEFS place precipitable water values around an inch on average across the area from mid-day Monday through the middle of Monday night. These values place the region within a plus two sigma regime for the precipitation. Given how dry the area has been recently, there are currently no flooding concerns in the short term during the event. In the longer term, a look at the MMEFS river ensemble forecast have their highest percentage for rivers to remain under action stage in the days following the rain event.

Confidence in the above portion of the forecast is moderate to high. The element with the least confidence is the type, location and amounts of any wintry weather.

LONG TERM /TUESDAY THROUGH SATURDAY/... As of 100 PM EST Saturday...

Another potential threat of wintry weather Wednesday into Thursday along with a return to below average temperatures for the workweek.

A cold front with several waves of low pressure along it will move east across the region Tuesday. The model solutions indicated a drying trend late Tuesday afternoon into Wednesday. The upper trof will curve into central U.S. Wednesday and pivots east across our region Wednesday night into Thursday. This will develop low pressure which will travel south of us Wednesday into Wednesday night and deepen off the East Coast Thursday. Low pressure will move east out in the Atlantic ocean Thursday night into Friday. High pressure will build south out of the Ohio Valley into our region Friday into Friday night. The high center will push east into the Atlantic ocean Saturday into Saturday night.

There remains some key differences between the global model solutions. The operational GFS still supports significant snowfall Wednesday night into Thursday. The placement of the low is further west and deeper. In contrast, the ECMWF indicated a slower and weak system with less snowfall. In any case, the models are highlighting some snow for the north and western mountains with some upslope possible on the northwest side of the coastal low.

The details of the next winter system will become clearer over time. Temperatures look to remain at or slightly below normal through the workweek. Then, temperatures will moderate for the weekend.

Confidence remains low to moderate through the long term period.

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