... A front will move slowly southward across the region today, with cooler air spilling in from the north. Moisture will return over the front tonight. Moisture will continue to stream over the front with rain becoming widespread Thursday into early Friday morning as a system lifts through the area. Dry and cold air will filter into the area Friday into the weekend with temperatures falling below average. Temperatures rebound late weekend into early next week.
NEAR TERM /THROUGH TONIGHT/... As of 1030 am EST: Most of the precip has ended across the fcst area this morning, save for a small broken band of light rain and sprinkles moving across the area north of I-40, and that looks like it will fall apart in short order. The main problem is the frontal boundary slowly moving south across the fcst area, which will have a big impact on the temps thru the afternoon. Some places over the northern part, in particular the NW Piedmont, may have already had their high temp for the day, while areas over the lower Piedmont have broken out of the clouds for the time being and are warming up into the lower 60s already. This puts us in the position of having to lower the fcst north and raise it south.
Otherwise, moist upglide will return over the frontal boundary tonight as a deeper moisture band moves back in atop the region. Temperatures again remain just warm enough across the northern mountains for all liquid with the returning precipitation overnight.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 159 AM EST Wednesday: Stubborn sub-tropical ridging centered over the Florida Straits will finally get shunted east as a positively tilted shortwave trough ejects through the Southern Plains and eventually into the southeast states. On the poleward side of the ridge, a belt of west/southwest flow aloft will extend across the Southern Appalachians ahead of the ejecting trough. This flow and associated plume of deep moisture will be juxtaposed atop a persistent baroclinic zone that has struggled to move in the face of boundary parallel flow and building heights from the ridge to the southeast. Showers will be ongoing across much of the area Thursday morning and will continue through much of the day. The highest rainfall rates will occur Thursday evening through the overnight hours as the right entrance region of an upper jet pivots overhead in concert with a band of frontogenesis amidst 1.25-1.5" PWATs. It is during this time that isolated flooding cannot be entirely ruled out along and south of I-85, but the progressive nature of the forcing and a lack of instability/convective rainfall rates will preclude a greater flooding threat.
A 1045mb high spilling into the Midwest will help usher in a much colder and drier airmass on Friday. It's possible that the leading edge of the cold air may catch the back edge of the departing precipitation across the mountains Thursday night with a brief period of wintry mix transitioning to an equally brief period of snow as the depth of sub-freezing air deepens. Even if this scenario is realized, it's unlikely that there will be sufficient QPF left to cause any impacts. Temperatures will be below average Friday, especially across the foothills and mountains. The surface high over the Midwest will quickly translate east becoming centered across eastern Virginia by Saturday morning. This will promote favorable conditions for efficient radiational cooling as the boundary layer decouples beneath clear skies in a dry airmass. Overnight low temperatures will crash into the teens across the mountains with low 20s elsewhere.
LONG TERM /SATURDAY THROUGH TUESDAY/... As of 246 AM EST Wednesday: Saturday will be the coldest day of the period with high temperatures running 10-15 degrees below average despite insolation. This shot of cold air will be short lived, however, with the airmass quickly modifying Sunday into early next week. Highs will remain a few degrees below average on Sunday but will return to above average by Monday. Temperatures aside, guidance has come into better agreement with the evolution of a northern stream trough diving out of the Northern Plains and into the Ohio Valley on Sunday. The GFS solution has trended in line with the rest of guidance and no longer depicts QPF response across the area as the system will likely be moisture starved along with forcing displaced farther north. Thus, will advertise a dry forecast through the weekend, but at least some degree of cloud cover will likely return on Sunday. Guidance quickly diverges by early next week as a trough gets carved out over the Desert Southwest. The GFS/ECMWF/CMC all show varying solutions with the eventual wave ejection and whether it briefly becomes cutoff. The national model blend brings low end rain chances back to the region Tuesday into Wednesday, which seems reasonable for now until guidance comes into better agreement.