... Low pressure will meander near Lakes Erie and Ontario through tonight. High pressure will build from the Midwest to off the southern Middle Atlantic coast Wednesday into Thursday. Another area of low pressure will likely approach from the Tennessee River Valley Friday into Saturday. High pressure will probably follow briefly before another storm system approaches early next week.
NEAR TERM /THROUGH TONIGHT/... The GOES-16 mid-level water vapor channel shows quite the closed upper low encompassing the lower Great Lakes/Ohio Valley into the Appalachian chain. Upstream temperatures underneath this cold core low are running in the upper 20s to low 30s. The leading edge of the forcing has already reached locations along and west of the Allegheny Front. A number of traffic cameras from these locations indicate snow has begun covering local highways. A Winter Storm Warning is currently in effect for Garrett County as well as western Grant and Pendleton Counties through 7 AM Wednesday. Meanwhile, Winter Weather Advisories are also in place over far western sections of Highland, Mineral, and Allegany Counties through 9 PM this evening.
While upslope trajectories are not quite orthogonal to the terrain, enhanced vertical motions with embedded shortwaves should prove instrumental to drop ample snow over the above highlighted region. Snow amounts approaching 10 inches are possible within the warning, with a broader 2 to 4 inches likely over higher elevations of the advisory. Initial snow production may initially be stunted by a lack of deep layer moisture. However, this should improve throughout the day with the heaviest amounts ending during the overnight hours.
Farther downstream, a couple of these shortwaves ejecting off the high terrain could bring a few spotty showers to areas east of the Blue Ridge. Given the amount of cold air aloft, an isolated heavier shower may even bring some flurries to the I-95 corridor. As this frontal surge moves through, a precipitous drop in temperatures will occur with highs stuck in the 40s. Brisk westerly winds are to accompany this cold blast with gusts around 20 to 30 mph at times. At times, wind chill temperatures may drop into the mid/upper 30s in the lower elevations. Heading into the overnight hours, enough boundary layer mixing will thwart any attempts at decoupling. Lows should bottom out in the upper 20s to low 30s, with upper teens to low 20s in the mountains. Interestingly, the cold air arrives just in time with the start of Meteorological Winter on December 1st.
SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... By Wednesday, the expansive negative height anomaly is forecast to lift into extreme southern Quebec. Trailing northwesterly flow could spawn a few lingering snow showers in the mountains to start off the day. Otherwise, a slight warming trend will ensue with brisk winds continuing for at least the first half of the day, accompanied by sunny skies. Mid-week temperatures are likely to run closer to 50 degrees in the metro hubs which is near seasonal averages. On Wednesday night, a strong dome of high pressure moves into southwestern Virginia. With this feature being displaced to the southwest, there should be enough wind overnight to keep temperatures from plummeting. Below freezing temperatures are again possible, with the notable exception being closer to the Potomac and Chesapeake Bay waters. Dry weather continues into Thursday with a transient shortwave ridge sweeping through. Further warming is expected with an increase in cloud cover late as warm advection ensues from the trough over the Ozarks. This increase in clouds also raises Thursday night's temperatures a bit.
LONG TERM /FRIDAY THROUGH MONDAY/... A block pattern is (still) forecast by virtually all of the medium range guidance through the weekend. The trend over the last 24 hours has been back to a slower and deeper low pressure area evolving out of the Tennessee River Valley toward the Middle Atlantic Friday into Saturday. There is just enough cold air in play to bring a threat of wintry weather near the higher terrain, but details are far from certain at this point.
High pressure looks slated to build into the region briefly Sunday before another system approaches early next week, but the details of that system are even less certain than the one Friday/Saturday.