... Low pressure will pass to the south tonight. High pressure will return late Thursday through Saturday before another area of low pressure affects the region Sunday into Monday.
NEAR TERM /THROUGH THURSDAY/... Clouds will increase again this evening ahead of low pressure approaching from the Tennessee River Valley. This area of low pressure will move off the South Carolina coast by Thursday morning. Although this surface low track is displaced well to our south, the parent upper-level trough forcing it will clip our area overnight into early Thursday morning. With cold temperatures through the atmosphere, precipitation will be mainly snow, and accumulating snow (albeit relatively light) is most likely along the Allegheny Front south of Canaan Valley, and across the foothills and surrounding valley/Piedmont areas of west-central Virginia near and south of the I-64 corridor. A light coating of snow is possible during the Thursday morning commute for many of the Washington, D.C. suburbs, particularly south of I-66. Recent 18Z guidance including hourly convective- allowing solutions have trended northward. As such, some areas north of I-66 across northern Virginia could see a light coating in this scenario. Given cold road temperatures, any accumulations which stick could pose commuting concerns for Thursday morning. For areas along and west of the Allegheny Front north of Canaan Valley, accumulation is not anticipated.
Some guidance has advisory-level snowfall (around 2 inches) along the Blue Ridge Mountains and atop Shenandoah Mountain, but the northwesterly flow (which is typically dry) plus the quick nature of the system have precluded the issuance of any Winter Weather Advisories at this time.
Conditions will clear by mid morning Thursday, but it will be quite chilly despite the increased sunshine. Strong cold air advection will result in high temperatures generally in the 30s, and when coupled with wind gusts of 30 to 40 mph, wind chill temperatures likely hold in the 20s all day.
SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... Thursday night through Friday night will likely be the coldest time period most of the area has seen in a couple years as Arctic high pressure builds toward the region. High temperatures in the 30s (teens on the mountains) coupled with a continued blustery northwesterly wind Friday is forecast to keep wind chill temperatures in the teens and 20s again. Overnight low temperatures are forecast to fall into the teens to lower 20s (single digits on the mountains) each night, with wind chill temperatures down into the single digits for most (single digits and teens below zero on the higher ridgetops).
LONG TERM /SATURDAY THROUGH WEDNESDAY/... High pressure initially located overhead will slowly start to slide offshore Saturday afternoon into Saturday evening. Dry conditions, a light wind, and chilly temperatures are expected for Saturday, with high temperatures in the 30s for most. The sky should start out mostly sunny, but high clouds will start to filter in later in the afternoon.
Beyond that, attention turns to a system currently located just off of the West Coast. This system will move onshore tomorrow, and track across the CONUS Friday into Saturday. By Saturday Night the system will move into the Ohio River Valley. As it does so, warm air advection precipitation downstream of the closed mid-level low/broader scale trough will start to overspread the area either late Saturday Night or early Sunday. Confidence is increasing that much, if not all of the forecast area will see at least some accumulating snow on Sunday in association with this round of warm air advection precipitation.
Confidence in the details of the forecast decreases thereafter. At mid-upper levels, the closed mid-level low is expected to very slowly progress toward the east Sunday Night through Monday as a downstream system over the Atlantic Ocean blocks its forward progress. Meanwhile, an additional disturbance descending down from the Upper Great Lakes in northwesterly flow will act to reinforce the backside of the trough as the first piece slowly progresses to the east. As the first piece progresses eastward, the primary surface low over the Ohio River Valley should eventually transfer to a developing coastal low off the Eastern Seaboard. Additional snow may be possible with this coastal low, but a lot of uncertainty remains with respect to the eventual strength and placement of this low pressure and its associated precipitation shield. Either way, at least some (snow) shower activity will remain possible on Monday, but the potential is also there for a more substantial snowfall with this round (as shown in the deterministic 12z Euro). Ensembles continue to signal significant spread during this time period, which illustrates the high level of uncertainty in the forecast for Sunday Night through Monday. Depending on how the downstream block evolves, snow showers may even linger into the day on Tuesday. We'll continue to assess trends and adjust our forecast as confidence gradually increases moving closer to the event.