Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 271855 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 255 PM EDT Mon Mar 27 2017 .SYNOPSIS...
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A cold front will cross the area late Tuesday. High pressure builds over the region Wednesday into Thursday. Another disturbance will approach the area late Thursday into early Saturday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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While it took some time...visible satellite imagery and surface observations indicate that the stubborn marine stratus layer has all but eroded from the area as warm front lifted northward into PA. As expected...this has led to a rapid warmup...with highs in most places well into the 70s by late afternoon (with even some U70s possible across central VA and the Shenadoah Valley). CAPE gradient sets up this afternoon roughly from Montgomery County to the south...with ~500-700 J/kg of MUCAPE (~250 J/kg MLCAPE) expected across central/northern VA into south central MD. Thus, could be a few scattered thunderstorms this afternoon across these areas along the differential heating boundary. 0-6 km effective bulk shear generally near 30-35 kts suggests a storm could briefly become somewhat semi-organized. Though, lack of deep quality moisture coupled with long skinny CAPE profiles and relatively weak winds aloft likely limit any stronger thunderstorms. Gusty winds and small sub-severe hail would be the primary threats in any activity this afternoon. Thunderstorm chances rapidly decline after sunset. Isolated (to perhaps scattered at times) shower chances continue through the overnight. Though, think most places will remain dry through much of the night. Best chance for precipitation arrives across the SW after midnight and then spreads NE through the morning as shortwave approaches. There could be some isolated thunder with this elevated activity. In addition...there could be some patchy dense fog tonight as we decouple and low-level moisture remains. Guidance continues to indicate the most likely location for fog would be from DC and to the NE.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
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Another warm day tomorrow as moisture/warmth pools ahead of cold front. SPC continues to delineate the southern half (i.e., from DC south) and east of the Blue Ridge in a marginal risk for severe weather. While CAPE is higher tomorrow (e.g., ~500-800 J/kg MLCAPE with the higher amounts to the south) shear is also considerably less (i.e., ~20-25 knots). Thus, expect the possibility of a few poorly-organized marginally-severe thunderstorms across the risk area. Any threats expected to be isolated and confined to damaging wind gusts and small hail. Chances for precipitation should be ending late Tuesday evening as the shortwave moves off the coast and cold front pulls away from the area. High pressure returns Tuesday night and Wednesday. Temperatures Wednesday cool nearly ten degrees from Tuesday (though still remain above normal).
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Thursday starts out dry as a high pressure builds into the NE CONUS. Meanwhile, a strong closed low will be moving northeast from the southern plains and into the Mid-Atlantic. This system will bring decent amounts of moisture into the region, with rain starting Thursday night and remain into sometime Saturday. Many GEFS members bring the highest QPF amounts on Friday night. Conditions become dry behind this system Saturday and into Monday. High temperatures will be in the 50s and 60s, and lows in the 40s.
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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VFR expected through the remainder of today...with perhaps a passing shower or thunderstorm this afternoon. Chance is too low to include in the TAF...but most likely terminals would be IAD/DCA/CHO. Dense fog is also possible at some of the terminals overnight. Best chances for fog or low clouds at IAD/MTN/BWI/DCA. Kept TAFs at IFR for now...though if fog does occur there could be some sub-IFR conditions. A chance for thunderstorms returns to the terminals Tuesday afternoon...with the possibility of gusty winds and small hail in the strongest storms. Conditions should improve late Tuesday evening through Wednesday with the return of VFR as high pressure builds into the area. Dry/VFR conditions expected for Thursday before rain approaches over the area Thursday night, possibly bringing sub-VFR conditions over the terminals Friday into early Saturday.
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&& .MARINE...
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SCA currently in effect for the southern portion of the waters through late afternoon. In addition, there is a low probability of an isolated thunderstorm with gusty winds late this afternoon. Thunderstorms will again be possible Tuesday afternoon, some of which could produce SMW-level winds. Wind gusts will then increase Tuesday night into Wednesday behind frontal passage...with SCA possible as early as early Wednesday morning...but likely during the day Wednesday. Winds expected to diminish later Wednesday. Dry conditions expected for Thursday before rain approaches over the area Thursday night bringing showers over the waters into part of Saturday. Wind gusts will be near the small craft advisory threshold mainly Friday night into Saturday... therefore SCA possible at times.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ533- 534-537-541>543. && $$ SYNOPSIS...MSE NEAR TERM...MSE SHORT TERM...MSE LONG TERM...IMR AVIATION...IMR/MSE MARINE...IMR/MSE

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