Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 282213 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 613 PM EDT Thu Jul 28 2016 .SYNOPSIS... A front will remain stationary along the Mason-Dixon line through Friday morning. An area of low pressure will ride along this front across the area tonight into Friday. The front will move offshore during the weekend, then high pressure will build in by early next week. && .NEAR TERM /THROUGH FRIDAY/... Thunderstorms ongoing with a line ahead of a cold front across PA. Temperatures have dropped fifteen degrees during the late afternoon where storms have occurred. South of the line temperatures are still in the lower to mid 90s. We are watching the other area of storms over eastern WV which are tracking east. Question is whether the intial line took so much energy out of the atmosphere that this next round will not have enough juice to do more than be rain/isolated thunderstorms. However the severe thunderstorm watch remains in effect until midnight. Overall threat should morph from severe to flood. Expanded Flash Flood Watch. See Hydrology section below for more info. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... Once low emerges from coast, which should be sometime Friday morning, there won`t be a lot of forcing for thunderstorms on Friday. However the front will still be nearby with embedded vort energy. Therefore its entirely possible that thunderstorms may return Friday afternoon. Will maintain chance PoPs for the afternoon and evening. Another shortwave will track across the area Saturday afternoon and evening. Anticipate that this afternoon`s scenario will repeat on Saturday, although the airmass likely won`t be quite as unstable. Current SPC outlook is for MRGL severe risk. Can forsee more heavy rain issues. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Quasi-stationary front remains near the area Sunday and will act as a foci for mainly afternoon/evening showers and thunderstorms in the warm (U80s) and humid atmosphere (dewpoints in L70s). Frontal boundary begins to sink southward as a "cold" front late Sunday into Monday with weak high pressure beginning to build into the area. This will act to keep temperatures near seasonable averages through much of the week. Proximity of frontal boundary just to our south keeps shower/storm chances in the forecast Monday (especially in the southern part of the forecast area). By Tuesday, front is forecast to move far enough south that shower/thunderstorm chances will be limited through midweek. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... There may be a second round of storms late this evening. Airports may still have low ceilings (MVFR) if it does. Worse case supports a continuation into the morning push Friday. A lull in activity expected Fri afternoon and night before more rain moves into the area Sat-Sat night. Stalled frontal boundary across the area Sunday will lead to showers and thunderstorms. Front sinks just south of the area Monday, though showers/thunderstorms are still possible (mainly for southern terminals). Front far enough south by Tuesday that shower/storm chances should be limited. && .MARINE... Marine Warnings likely near thunderstorms. Winds strengthen late tonight and especially Friday as deepening low pressure departs the area. A Small Craft Advisory remains in effect for the Chesapeake Bay and lower Potomac for Friday. Frontal boundary remains across the area Sunday, with thunderstorms possible into Monday. Any storm could produce gusty winds over the waters. && .HYDROLOGY... Moisture rich air converging upon a boundary across the northern half of the forecast area this afternoon. Precipitable water levels up to around 2 inches. Storms that have developed have been producing rainfall in that range. Although antecedent conditions have been quite dry, the rainfall rates in warm rain processes appear to be sufficient to overcome this obstacle. This rainfall will be enhanced by a shortwave crossing the area this evening. Therefore, expect periods of moderate to heavy rain through the period. Have expanded Flash Flood Watch for northern 2/3rds of the area, consistent with where best ingredients reside. It is uncertain how long this threat lasts. HRRR has been consistent in depicting the final wave crossing area through midnight. On the other hand, GFS/ECMWF keeping threat through Friday morning. Am erring on the longer side for the watch. Will monitor situation, and cancel early if warranted. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Flash Flood Watch through Friday morning for DCZ001. MD...Flash Flood Watch through Friday morning for MDZ003>006-011- 013-014-501>508. VA...Flash Flood Watch through Friday morning for VAZ026>031-040- 052>054-501-503>507. WV...Flash Flood Watch through Friday morning for WVZ050>053-055- 501>506. MARINE...Small Craft Advisory from 7 AM to 6 PM EDT Friday for ANZ530>534-537>543. && $$ UPDATE...WOODY! PREVIOUS...HTS/MSE/JCE is the U.S. government's official web portal to all federal, state and local government web resources and services.