Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 240046 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 846 PM EDT Thu Jun 23 2016 .SYNOPSIS... A low pressure system will move east across the region tonight and Friday. High pressure will build in from the north Saturday and Sunday. A cold front will cross the region early next week. && .NEAR TERM /THROUGH FRIDAY/... Surface features are diffuse at this time, but numerous strong to severe thunderstorms have been feeding off of a stalled boundary across southern Virginia and West Virginia. That area has high CAPE values (3000 j/kg per recent mesoanalysis) as well as precipitable water values approaching 2 inches. Although shear has been high locally, mean layer instability and forcing have been lacking, in addition to a dry mid layer. A few showers and thunderstorms have been able to develop in late day heating across southern Pennsylvania, and these may clip northern Maryland this evening. Otherwise, there isn`t much radar activity at the present time. There is too much precipitation too close to the Central Shenandoah Valley/adjacent eastern West Virginia panhandle to pull PoPs there, but have scaled back. If current trends hold, we will be able to let the Flood Watch drop at 10 pm. Overnight, patchy fog may develop in many areas. Approaching trough may also keep some showers or isolated thunderstorms going through the night. Am limiting that potential to south of a Petersburg WV to Fredericksburg VA line. Lows will be in the 60s. Friday, the upper level trough passes through and the front should still be lingering especially in central VA. There may be enough forcing and CAPE to trigger some additional strong to severe thunderstorms but uncertainty is high. Best odds favor central VA on south. Highs should rebound into the 80s. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... High pressure will push southward into the region Friday night and dominate through the weekend as the center shifts eastward to our north. Any lingering showers should die out Friday night. Generally dry Saturday though lingering moisture and easterly upslope flow along with heating may spark a shower in the mountains. Sunday looks completely dry as ridge aloft builds directly overhead. Warming trend will develop Sunday though tempered by a somewhat easterly flow. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... High pressure will remain in control into early next week. 590+ DM 500 MB heights suggest decent heat. Warm and humid conditions briefly envelop the region Monday before a cold front moves in from the west, which may trigger a round of scattered showers and thunderstorms. High pressure and seasonably cooler temperatures will return for the middle part of next week. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... VFR conditions prevail at the terminals this evening. Don`t believe showers and thunderstorms will be an impact. There`s a continuous line south of CHO, with additional scattered activity north of MTN. The northern batch should dissipate before midnight. While the southern activity will last longer, it too will weaken while remaining south of the area. Patchy fog may reduce cigs and vis later tonight into Friday morning. Low levels are humid, but am uncertain how much radiational cooling we will see. Focused more on vsbys vs cigs, assuming that there will be thin spots in cloud decks that aren`t all that low just yet...taking a predawn period of IFR at climo preferred locations (IAD/MRB/CHO) and MVFR elsewhere. IFR could be more widespread, and LIFR possible. However confidence in a more drastic solution lacking at this time. Thunderstorms may redevelop Friday afternoon. Don`t have a good feel for specifics yet, so aside from P6SM -SHRA at CHO have mainly kept the risk out of the TAFs at this point. Fog may redevelop again late Friday night into Saturday morning before air mass can dry out. After that, VFR should prevail through the rest of the period. && .MARINE... Due to ongoing cloud cover, winds have been below 10 kt for the most part. Expect sub-SCA conditions this evening through Sunday as high pressure slowly builds in from the north. However, showers and thunderstorms will remain possible again on Friday with SMW`s possible. Storm-free Saturday and Sunday. Southerly channeling and small craft conditions possible Monday ahead of a cold front. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...Flash Flood Watch until 10 PM EDT this evening for VAZ025-026- 036>038-503-504-508. WV...Flash Flood Watch until 10 PM EDT this evening for WVZ505-506. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...HTS/RCM SHORT TERM...RCM LONG TERM...DFH AVIATION...HTS MARINE...HTS/RCM/DFH is the U.S. government's official web portal to all federal, state and local government web resources and services.