... Expansive high pressure over the southeastern states will gradually shift offshore Thursday. A pair of cold fronts will cross the area Thursday night through early Saturday. High pressure will build nearby over the weekend, but the next frontal system may approach by Sunday night.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... High pressure will remain centered to the south tonight, resulting in more dry conditions. The gradient will be light enough for many locations to decouple, causing more radiational cooling. However, a milder start relative to recent days along with slightly higher dewpoints does mean that tonight will not be as cool as recent nights. Lows will still be in the 40s for most areas with 50s on the ridges, urban centers, and nearshore areas.
SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Thursday will remain in the same regime for much of the area as the surface high begins to depart offshore and a low pressure center migrates across the Great Lakes. While there may be a few more clouds, it will still be unseasonably warm under the influence of a southwest wind, with some locations potentially near or above 80F. Ahead of the trailing cold front, some showers and storms are expected to develop over the Ohio Valley, approaching the Appalachians by mid to late afternoon. While there will be some shear present, already-weak instability will taper rapidly from the Ohio Valley to the Appalachians, as well as with the onset of nocturnal cooling. Therefore any storms will be in a weakening state as they reach our forecast area, and in fact, most of the activity will likely fall apart crossing the mountains due to weak/displaced forcing and a downslope component to the flow. However, a few showers may survive to the Blue Ridge and across northern Maryland during the evening/early night. The cold front will push through overnight, and a secondary shortwave from North Carolina could produce a shower or two across southern Maryland.
Broad upper troughing will develop over the eastern CONUS by Friday, with a secondary front and shortwave trough approaching the area Friday night. Increased cloud cover is likely, although most of the time will be dry. The greatest chance of any showers will be across southern Maryland and the Appalachians, which will be closer to notable but still weak forcing mechanisms. Temperatures will be cooler behind the first frontal passage, but will still likely be a little above normal for this time of year.
LONG TERM /FRIDAY THROUGH WEDNESDAY/... Heights will rise slightly as the broad trough moves to the northeast Saturday into Sunday. At the surface, high pressure will build across the Ohio/Tennessee Valley late Saturday and expand northeast into early Sunday promoting dry conditions. Saturday night continues to look favorable for radiational cooling especially away from the Chesapeake Bay and metros. The cooler locations of the western CWA could fall into the low to mid 30s resulting in at least patchy frost. By late Sunday, WAA will move into the region so have maintained slight chance POPs over most of the region to account for showers.
Uncertainty still remains heading into early next week with how the shortwave trough ejecting out of the central Plains evolves as it continues moving east. Some guidance depicts a closed upper level low moving near or south of the region, while other guidance supports a more sheared solution of a broad shortwave moving through. Regardless, have maintained slight chance to chance POPs to account for the model uncertainty Monday into Tuesday. Temperatures will be highly dependent on the evolution of the aforementioned trough.