Multiple lows will impact the region through early Monday morning. High pressure builds in through the early parts of next week before another system potential impact our region on Wednesday.
NEAR TERM /THROUGH SATURDAY/...
High pressure is currently situated along the astern seaboard of the mid-Atlantic and is expected to continue moving slowly eastward. As the high moves off the coast, winds will become more east to southeasterly throughout our region leading to weak moisture advection. The northern half of our region briefly experienced periods of clear skies this morning as a shortwave dropped south of our region but the outer cloud decks of a approaching low are now moving northward into our region this afternoon. Afternoon temperatures are still on track to peak in the mid to upper 40s to low 50s.
As the high moves east of the coast this afternoon, weak cold air damming is forecast to occur along the eastern half of the Allegheny front. A low pressure system will approach from the south and track through the southern half our region late this evening and into Saturday. Ahead of this system, overruning precipitation will move into our central Virginia counties over the next few hours and slowly spread northward this evening. The precipitation should begin as rain or rain/snow mix and then transition to all snow from 0Z to 4Z on Saturday. A warm layer may lead to mix precipitation early Saturday morning which may allow for a wintry mix with a focus on sleet with periods of freezing rain. As of right now I believe the freezing rain threat is very limited with the area with the best chance being along the eastern half of the Allegheny front. Generally, i'm expecting snow totals of 1 to 3 inches with locally higher amounts along our higher elevations in central Virginia.
By four to five am on Saturday, all precipitation is expected to have transitioned over to all rain as temperatures rise above freezing with the heaviest axis of precipitation slowly shifting northeastward toward northern and eastern Maryland. The coastal low that moves through our region should start pulling away from our region Saturday morning. Rain will taper off during the middle parts of Saturday morning with only a few lingering showers into the early afternoon periods. Mostly dry conditions expected Saturday afternoon and into early Sunday morning with Saturday afternoon temperatures rising up into the mid to upper 50s.
SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
A second frontal system will move into the northern half of our region late Saturday and into Sunday. The front will become stalled over our region through Sunday with multiple lows forming and moving along the boundary. Precipitation should start impacting our region early Sunday morning with precipitation becoming widespread by the middle parts of the morning. Winds will be light and out of the south at the surface with a southwesterly flow aloft. The southwesterly flow aloft will have a slight downsloping component which will help limit some of the precipitation that falls east of the Allegheny front. The heaviest precipitation looks to occur along and west of the Allegheny front and likely occurs Sunday afternoon. This boundary will remain near our region into Monday morning with an extended period of light to moderate rain expected.
Flooding will be a concern with this system as some areas in western MD and along the Allegheny front still have a decent snow pack which combined with heavy rain may add a fair amount water to our rivers. The Mid-Atlantic River center currently has a few of our river points along the south branch Potomac reaching close to minor flood stage late Sunday and into Monday morning. We will need to monitor the changing situation.
LONG TERM /MONDAY THROUGH FRIDAY/...
Light rain will be exiting the fcst area Monday morning as cold front presses south. Turning breezy/windy Mon afternoon and night as pressure gradient tightens between low pressure over the NW Atlantic and high pressure building from the Great Lakes.
Another low pressure will lift from the Mid-South Tue night and spread precip into the area Wed. Some of it could be on the wintry side if it arrives early enough and reaches far north. The higher elevs of Skyline Drive, Highland and Pendleton Counties would be the greatest at risk of any wintry precip.