Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211901 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 301 PM EDT Wed Jun 21 2017 .SYNOPSIS...
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High pressure will remain west of the area through Thursday. A cold front will cross the area late Friday night into Saturday, with tropical moisture streaming into the Mid Atlantic ahead of the cold front.
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The trough axis presently over New York and Pennsylvania this afternoon. A line of thunderstorms can be noted at the base of the trough. There are also a few showers and perhaps a thunderstorm from around Fredericksburg across southern Maryland to the eastern shore. This area received sufficient heating to reach convective temperatures. There is also more than ample effective shear (50 kt) in this zone as well. Did increase PoPs to accommodate these trends. Believe that this activity will be largely diurnal, and am forecasting a rapid decrease by sunset. We will be in ridging/subsidence in the wake of the trough tonight. Suspect there will be enough mid-level moisture for some clouds, but not enough for a solid cloud deck. We will have a dewpoint gradient overhead, which will influence low the 60s.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... For the most part, ridging will hold for the day on Thursday. However, warm advection/isentropic lift will be knocking on the door of the western ridges by afternoon. Add in terrain circulations, and have chance PoPs for the mid-late afternoon hours. Believe we will be a degree or two warmer for high temperatures, which places highs around 90 degrees. There are two windows of opportunity for heavy rain: Thursday night into early Friday and again Friday night. The former will be on the nose of the theta-e ridge. Precipitable waters will rise to in excess of 2 inches inside the ridge axis. Then, assuming even some clearing, there will be the opportunity for some significant instability to develop. While this is conditional, GFS MUCAPE progs indicate 1500-2500 j/kg possible. This will be in a sector with a 30-35 kt 925-700 mb jetlet and 500 mb flow reaching 55 kt, so more than ample shear will be present as well. We will keep to see how details pan out, but severe weather threats will need to be monitored over the next day or two. The second window of heavy rain/storms would be associated with the cold front that drops toward the forecast area Friday night. Given the possibility for saturated soils and prolific warm rain processes, this would be the period that flood concerns most likely will need to be assessed in the cycles to come. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... A cold front, likely entangle in the remnants of Cindy, will move away from the area early Saturday. This should lead to much drier and more comfortable (less humid, warm but not hot) conditions for much of the weekend. A secondary cool front may drop through the area early next week, which should keep near to slightly below normal temperatures and humidity through at least the middle of next week. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... VFR conditions anticipated through Thursday. Showers and perhaps some thunderstorms will approach Thursday night. Friday and Friday night look unsettled as moisture from the remnants of Cindy stream northeast ahead of a cold front. Local flight restrictions likely, but its difficult to time specifics at this point. Sub-VFR likely Sat AM, then VFR through Sun. Patchy fog possible Sat night. Winds W 5-10 kts. && .MARINE... Southwest flow under Small Craft thresholds this afternoon. However, there are a couple of showers/maybe a thunderstorm near the waters which may contain gusty winds. A couple of Marine Warnings may be required. Some mesoscale guidance suggesting the southerly channeling may occur again tonight on the mid-Bay. If it happened, it would be a few gusts to 20 kt for several hours. Have limited forecast just under Advisory criteria at this time. Will pass concerns on to the next forecaster. A similar wind regime will continue through Thursday night. Gradient flow increases by Friday as the remnants of Cindy stream north ahead of a cold front. Small Craft Advisories seem likely at this time. Gusts should subside quickly Saturday and remain below Small Craft Advisory levels through the rest of the weekend. && .TIDES/COASTAL FLOODING... Water levels a few inches above astronomical normals this afternoon. These will slowly increase over the next couple of days. There is the potential for minor flooding by Friday at sensitive sites, in the gradient flow ahead of a cold front which would be merged with moisture from the remnants of Cindy. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...DFH AVIATION...HTS/DFH MARINE...HTS/DFH TIDES/COASTAL FLOODING...HTS is the U.S. government's official web portal to all federal, state and local government web resources and services.