Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 271924 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 324 PM EDT Sun May 27 2018 .SYNOPSIS... A stationary front will stall across our region before dissipating during the middle of the week. The remnants of Alberto may pass west of the region later in the week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... As of 3 pm, heavy showers and strong thunderstorms producing torrential rain continue to move west to east across our CWA along a stalling frontal boundary. Multiple flood and flash flood warnings have been issued with additional warnings expected later this afternoon and this evening. A Flash Flood Watch has been extended for a large portion from northeast Maryland southwest into the Virginia Piedmont through 2 am tonight with added zones in southern Maryland, western and central Maryland, eastern West Virginia, and northern Virginia, as well. Precipitable water across our region has been in the 1.8 to 2.2 inch range during the afternoon and will likely linger within this range into mid-evening. Although we anticipate some showers and thunderstorms to linger late this evening and overnight, the bulk of the heavier activity is expected to diminish in intensity and coverage. && .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... High pressure building in from the north behind the stalled front will bring in some stable air to reduce the shower and thunderstorm threat Monday; however, the forward push of the high might not be enough to wash-out the stalled front. Therefore, the chance for more showers and a few thunderstorms will continue Monday into Monday evening. As for Tuesday and Tuesday night, weak high pressure may try to bring more reinforcing drier air into the region. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... The latest National Hurricane Center forecast has the remnants of Alberto tracking through the Western Ohio Valley and across central portions of the Great Lakes Wednesday through Thursday. Southerly flow between Alberto`s remnants and an area of high pressure centered off the New England coast will transport a moisture rich air mass into the region, with precipitable water values approaching or exceeding 2 inches by Wednesday Night and Thursday. Showers and thunderstorms will be possible each day in the extended period with the moisture rich air mass in place. The best chances for focused heavy rainfall will be Wednesday afternoon through Thursday. Wednesday will feature low values of CAPE compared to following days, but we will be located downstream of Alberto`s remnant mid-level circulation, providing slightly more large-scale forcing for ascent. With Alberto`s remnants tracking well off to the west, an easterly component to the low-level winds on Wednesday could enhance rainfall along the Blue Ridge. Thursday will feature much higher levels of instability, but Alberto`s circulation is progged to be located over the Great Lakes by then. The combination of higher instability and a more subtle shortwave approaching in westerly flow to the south of Alberto`s remnants should spark some showers and storms. Additional storms will be possible Friday and Saturday with a trough hanging back to our northwest, but details remain hard to pin down this far out. Temperatures look to remain above normal throughout the long term period. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... MVFR conditions for the terminals in showers and thunderstorms through this evening. Most of the thunderstorm activity will continue through 00z. Light southwest winds. As the front stalls near CHO to southern MD, IFR CIGS likely tonight again. Light/variable to light NE flow. Lower CIGS could linger well into Monday with low level moisture firmly in place. Otherwise, a shower or thunderstorm is possible INVOF the front stalled over central VA Mon-Tue. Showers and thunderstorms will be possible at times Wednesday afternoon through Thursday as low pressure moves west of the area. Sub-VFR clouds and/or fog could occur during the overnight periods as well. && .MARINE... Generally flow will be light southwest on the south side of the boundary into early in the week. Showers and thunderstorms with frequent lightning and perhaps a few wind gusts are likely this evening, less likely Mon- Tue but non-zero chance with the front stalled nearby. Southeast winds may near SCA thresholds on Wednesday as high pressure moves off the New England coast and low pressure moves into the Ohio Valley. Thunderstorms will be possible from Wednesday afternoon through Thursday as the low remains to the west and draws moisture into the area. && .HYDROLOGY... A Flash Flood Watch remains in effect until 2 am Monday for much of Maryland, eastern West Virginia and about the eastern two- thirds of Virginia. Training convection seems most likely in these areas given enhanced surface convergence, with high rain rates expected due to PWATs near 2 inches and warm cloud layers of 12+ kft. Convection should gradually wane this evening with the loss of heating. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Flash Flood Watch until 2 AM EDT Monday for DCZ001. MD...Flash Flood Watch until 2 AM EDT Monday for MDZ003>006-011-013- 014-016>018-502>508. VA...Flash Flood Watch until 2 AM EDT Monday for VAZ027>031-038>040- 051>055-501-502-505>507. WV...Flash Flood Watch until 2 AM EDT Monday for WVZ050>053-055. MARINE...None. && $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW/DHOF LONG TERM...ADS AVIATION...ADS/KLW MARINE...ADS/KLW HYDROLOGY...KLW is the U.S. government's official web portal to all federal, state and local government web resources and services.