Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
305 FXUS61 KLWX 232121 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 521 PM EDT Sun Jul 23 2017 .SYNOPSIS... High pressure remains off the southeast coast. A weak boundary will remain near the area through Monday before stalling south and east of the area Tuesday. An upper level trough of low pressure will move over the northeastern US early in the week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
-- Changed Discussion --
Update... Initial showers/thunderstorms tracked to the Delmarva by mid afternoon. However, an additional impulse behind that fed upon 1000-1500 J/kg MLCAPE air with around 30 kt of effective shear...blossoming into another cluster of thunderstorms tracking across Maryland. While there has been forward movement, there have also been repeated cells. Further, RAP/HRRR both hinting at another round of showers/thunderstorms possible in the 03-06 UTC timeframe. Have therefore issued a Flash FLood Watch between Washington and Baltimore, including Baltimore metro, until the early overnight hours. Would not rule out local severe weather this evening. Otherwise, it appears as though hydro may be the bigger concern tonight. CAM suggestions are that there will be a break in the early evening, and then this activity will wane after midnight, with little precip during the overnight hours. Previous Discussion... MCV which was mentioned in the morning AFD update has been the primary player thus far as it has traversed across the southern half of the forecast area. Recent radar/satellite trends continue to show an area of showers and a few thunderstorms increasing in intensity as it moves east of DC toward the eastern shore of MD. Expect heavy rain and gusty winds with this activity as it pushes east...over the next hour or so. Forcing for ascent becomes far more nebulous behind MCV...with some subsidence noted in satellite imagery. However, area still remains very am expecting at least isolated-to-widely scattered redevelopment through the evening (perhaps into the overnight) where airmass can recover. Once such location may be across central VA this afternoon...where full sun has returned and visible satellite imagery shows some agitated cumulus developing. While severe threat has lessened as destabilization was hampered by cloud cover...scattered strong winds with isolated pockets of damaging wind are still possible in the strongest storms. Additionally, PWATs 1.75-2 inches coupled with recent rainfall continue to heighten concerns for localized flooding. Currently believe the threat this afternoon is too localized and tied to meso-beta influences to warrant a Watch. However, repeated rounds of rainfall over the same area (especially as we continue into tonight) could increase hydro concerns locally. Evening shift will continue to monitor this. As cover has helped to keep temperatures a few degrees cooler than yesterday...which have kept heat indices AOB 100F.
-- End Changed Discussion --
&& .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/... Frontal boundary will finally try to push through the area Monday. Most guidance continues to be stubborn with convective coverage...though believe at least isolated showers and storms are possible as the front encounters a warm and unstable airmass. The strongest storms would be capable of gusty winds and locally heavy rainfall. Some improvement from the heat front stalls to the S/E of the area. High temperatures will generally top out in the mid to upper 80s. Dewpoints will fall back into the 60s...which should feel more pleasant after the extended stretch of hot and humid weather. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Wednesday should be the pick day of the week with high pressure centered over New England, and extending down over our region. That should keep temperatures slightly below normal, and humidity in reasonable check with dewpoints in the 60s. By the time we get to Thu, the high has slipped off to the east and southwest flow returns with a rebound in temps and humidity. Late in the week, probably Friday, our next cold front is slated to push through from the northwest. Current indications are that it will stall just offshore with an area of low pressure forming along it off the Delmarva Sat and Sun. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/... VFR conditions will prevail through Monday...outside of isolated thunderstorm activity. Thunderstorms are possible this afternoon and evening with gusty winds and reduced visibility in the strongest storms. An isolated storm is also possible Monday...though most sites should remain dry. VFR returns Tuesday. VFR conditions expected Wed and Thu. Lowered vsbys and cigs are possible on Friday from the expected cold front with its showers and thunderstorms. && .MARINE... Winds will remain below SCA values through Monday. However, thunderstorms capable of producing gusty winds above Special Marine Warning criteria are possible today and perhaps on Monday. No marine hazards Monday night or Tuesday. Other than thunderstorms (most likely on Friday), no widespread marine threats are anticipated Wed through Friday. && .LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...Flash Flood Watch until 3 AM EDT Monday for DCZ001. MD...Flash Flood Watch until 3 AM EDT Monday for MDZ004>006-011-013- 014-503>508. VA...None. WV...None. MARINE...None.
-- End Changed Discussion --
&& $$ SYNOPSIS...MSE NEAR TERM...MSE/HTS SHORT TERM...MSE LONG TERM...CAS/MSE AVIATION...CAS/MSE MARINE...CAS/MSE is the U.S. government's official web portal to all federal, state and local government web resources and services.