... Surface and upper-level ridging builds across the region today into Thursday. Strong low pressure system builds into the area by late Thursday Night into Friday from the southwest, bringing several potential impacts to the area.
NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Weak high pressure is settling over the area this evening. Winds have been steadily declining from a combination of nocturnal stabilization and lesser influence from strong low pressure off the coast. Some stratus clouds exist on the fringes of the CWA: moisture from the Great Lakes banked against the western slopes of the Appalachians in northwest flow; and moisture on the outer fringes of the offshore low across southern Maryland. Other than these locations, the night should be mostly clear until some cirrus start increasing late ahead of the next trough. Temperatures in most locations will be in the 40s, with some 30s possible in the mountains/deeper valleys, and lower 50s in urban centers/nearshore areas.
SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... Thursday morning looks to have fairly tranquil conditions aside from clouds continuing to build in from the SW. High pressure will still be nearby early Thursday before a large upper-level trough out west of the area produces a cut-off low that will begin to move into the area. An associated intense surface low will progress northeastward Thursday, during the day. An attached warm front will move through the area late Thursday, bringing an initial wave of moisture into the southwest zones by Thursday night.
The bulk of the precip appears to come through during the day on Friday from SW to NE in the area. 12z guidance has come in a bit wetter for the period, with 1-2.5 inches expected across much of the area on Friday. A Slight Risk for excessive rainfall is present during the day on Friday. Flood Watches may be needed for more sensitive areas on Friday. Expect precipitation to last into Saturday morning before conditions begin to vastly improve.
In terms of potential severe weather, the threat looks to be fairly minimal with a stable airmass expected ahead of the system passage. The other impact for the system would be increased winds for much of the day on Friday. With impressive onshore flow wind fields, some of the higher terrains may see gusts 40 to 50 knots. High Wind Watches/Warnings are possible for these higher elevations on Friday. With water temperatures still being a bit warmer than the surface temps, winds will mix down a little easier over the waters and lead to increase potential for Gale-force winds across all of the waters on Friday.
LONG TERM /SATURDAY THROUGH WEDNESDAY/... A large area of low pressure at the surface and aloft will be overhead Saturday, resulting in cloudy skies and elevated shower chances. Temperatures will hover near to slightly below normal during this time thanks to the increase in clouds and rain chances. The axis of the upper low will begin to lift northeastward Saturday night into Sunday, as rain chances diminish with high pressure over central U.S. building eastward. Weak high pressure will be in control Monday with dry and seasonable conditions before the next frontal system approaches to our northwest Tuesday, bringing an increase in rain chances and temperatures remain near normal.