... A front will stall out near the Appalachians into southern Virginia through tonight. The front will then try to lift north as a warm front early Sunday, before a cold front moves through from the west late Sunday. High pressure will be in control Monday into Tuesday. A low pressure will then approach from the southeast U.S. Tuesday night before departing off the mid- Atlantic coast on Wednesday.
NEAR TERM /THROUGH SUNDAY/...
Biggest challenge for tonight is going to be how low cigs get and how low visiblities drop. Short-term guidance is all over the place with MOS guidance suggesting vsbys remain in the 2-4sm range while GLAMP and other hi-res models indicating visibilities dropping to less than half a mile. Not expecting any measurable precip other than some light drizzle.
SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
Short-term models like the HRRR indicate isold supercell potential possible especially along and north of Interstates 68 and 70. Even if warm front fails to lift into PA, there appears to be sufficient elevated instability that supercells could still produce large to very large hail. Convective initation remains questionable especially in southern areas where there is lack of frontal convergence. Isolated to scattered thunderstorms are still expected in the northern half of the fcst area.
Sunday will start with ample low clouds and fog attempting to lift. How quickly it does so may be the key to the forecast. Believe there will be a sharp inversion, with a warm nose which could be as warm as 19C near 925 mb.
A cold front will approach during the day, and cross the region during the afternoon, during peak heating (18-00 UTC). There will be ample shear across the region. Instability will be the question. If the wedge holds, then instability will be minimal and the front would either come through dry or as a few showers (with perhaps an elevated rumble of thunder). But, if the wedge does manage to mix out, then MUCAPE may exceed 1000 j/kg. Given the other ingredients in place, that would be supportive of robust thunderstorms. There are guidance members on each side of the fence.
After collaboration with SPC, decided that the conditional threat great enough to at least mention somehow...hence Marginal Risk of severe. Am maintaining a chance of precip crossing the area in the database, with a slight chance of thunder. It may be that both solutions are correct; ie: cool/stable air across northern Maryland while moist/unstable air present across central Virginia and southern Maryland. Will be monitoring later cycles to discern these details.
Sunday night into Monday a deep cyclone will build across the Great Lakes. The area will experience high pressure but westerly flow and cold advection. Lows will be in the 40s again by Monday night.
LONG TERM /TUESDAY THROUGH SATURDAY/... An upper level trough over the southern Plains will drop southward through the southern parts of the mid-Atlantic and the Carolinas Tuesday into Wednesday. A surface low associated with this trough will move to our south Tuesday afternoon and into Wednesday morning. The main area of precipitation should be situated to the south of our forecast area over the Carolinas and the southern portions of Virginia. As the main forcing remains to our south, the precipitation that we observe in our region will likely be caused by a combination of overrunning precipitation and an easterly flow off of the ocean. If this system tracks further northward, our region has the potential to experience heavier precipitation mainly late Tuesday and into Wednesday morning. Precipitation and an easterly flow will lead to daytime temps running near to slightly below normal for this time of the year in the 50s and lower 60s with overnight lows in the 40s
High pressure builds into our region behind the exiting low Wednesday afternoon and remains over our area through Thursday. Light winds out of north will lead to cooler conditions over our area. Temperatures will continue to hover in the 50s with overnight lows in the 40s on Thursday.
Another cold front is forecast to approach and move through our region Friday and into early Saturday. Models have some decent agreement on the subtropical jet moving northward and phasing with weak jet over the midwest and mid-Atlantic. This phasing will combine with a frontal passage to bring precipitation to our region once again. The main limiting factor will be a westerly flow transporting drier air into our area. We will need to monitor the strength of the jets to determine further hazards for end of next week.