... A weak cold front will pass through our region this morning with high pressure returning for this afternoon through Sunday. A strong storm system will impact our region late Sunday night through early Tuesday. High pressure builds back into our region from the south through the middle part of next week.
NEAR TERM /THROUGH SUNDAY/... Latest analysis shows a cold front just to our northwest at present. This front will cross the region this morning, with increasing sunshine and wind behind it for the afternoon. Thus, though there will be more sun this afternoon compared to yesterday, the increased wind may make it feel a little cooler. While an upslope rain shower or drizzle is possible along the Allegheny Front early this morning, any precip should end by midday.
A cooler air mass tonight will bring temps down closer to normal for tonight, with sub-freezing temps in many rural areas and 30s in the urban centers. Light winds and clear skies will help promote this cooling.
Sunday starts sunny, but we start to see some increasing clouds later in the day as the storm near the Gulf Coast strengthens and approaches. Highs will again be in the upper 50s, just like today, but with less wind, it likely feels a little more pleasant.
SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... Very active period Sunday night through Monday night. Strengthening trough cutting off into a closed low to our southwest Monday into Monday night will promote rapid surface low development, with the surface low rapidly propagating from Mississippi Sunday evening to western New York by Monday evening. Strong warm advection/isentropic lift on Sunday night/Monday morning plus excellent divergence aloft and strong southerly flow bringing very moist air northward should promote widesprad rain late Sunday night through Monday morning. Rain tapers to showers Monday afternoon, but the potent cold front and instability plus very high shear may result in a band of gusty showers and thunderstorms crossing the region during the afternoon. Combined with the morning rain, these storms could also promote a marginal flood risk. Even without the storms, strong southerly winds could approach 40 knots in parts of southern Maryland. Behind the cold front, showers linger with the upper level system approaching, while upslope flow and rapidly falling temperatures will promote rain changing to snow showers along the Allegheny Front, with a few inches looking probable. Winter weather advisories are anticipated for our westernmost zones. More details will be forthcoming as we approach the event.
Highs Monday reach the 60s east, 50s west, then temps fall into the 20s and 30s Monday night.
LONG TERM /TUESDAY THROUGH FRIDAY/... A robust upper low should be centered in the vicinity of the Kentucky/West Virginia border on Tuesday morning. This is the result of an earlier phasing with a southern stream shortwave. Recent guidance has backed off on keeping this system quasi- stationary in nature as it projects a northeastward push into southern Quebec by mid-week. Impressive height anomalies accompany this sprawling closed low with 1.5 to 2 sigma departures from early December climatology. As this trough sweeps overhead on Tuesday, 700-mb temperatures are likely to drop into the -10 to -15C range which would support the coldest temperatures of the season. Prolonged deep- layered west to west-northwesterly flow will support a steady period of upslope snow showers across the Allegheny Front. Thermal profiles are well below freezing with saturation up to at least 500-mb on Tuesday. Moisture is somewhat scant in nature but upslope processes should maximize the snow potential through Tuesday night. Drier air aloft will work into the region during the overnight hours with the upper low lifting away toward New England. Thus, snow shower production should halt at this point. While numbers will adjust over future forecast periods, a broad 3 to 6 inches of snow is possible along and west of the Allegheny Front.
From mid-week onward, a shortwave ridge sets up aloft as heights lower again across the nation's mid-section. This will ensure a period of drier weather through the conclusion of the work week. While surface high pressure maintains its presence through early Friday, global ensembles show upstream troughing ejecting eastward bringing additional rainfall chances into next weekend. This supports the Day 6-10 CPC Precipitation Outlook which highlights above average precipitation chances December 3-7.
High temperatures on Tuesday and Wednesday will top out in the 40s across most locations with upper 20s to 30s in the higher elevations. While westerly winds will provide downslope warming effects, the accompanying 15 to 20 mph gusts should lower wind chill temperatures into the mid/upper 30s on Tuesday along and east of I- 95. Overnight temperatures on Tuesday and Wednesday nights are likely to be at, or below freezing everywhere outside of spots near the Chesapeake Bay and Tidal Potomac. While chilly in nature, all readings are close to, or slightly below seasonal norms. A gradual warming trend is expected by late in the week.