Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 180800 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EDT Sat Mar 18 2017 .SYNOPSIS...
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Low pressure and associated cold front will move through the area late this afternoon. High pressure builds over the area early next week. Another cold front will cross the area Monday night.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Warm air advection precip will be ending in the next couple of hours if not by 12Z. Some drizzle and/or areas of fog are possible over the higher elevs. Main wx maker this afternoon and tonight will be an upper low over the upper midwest that will be digging southeast next 24 hrs. Upper level divergence and strong height falls (150 meters/24 hrs) will help trigger convective showers later today into early Sunday. An inverted sfc trof also sets up across the area tonight increasing sfc convergence with showers expected through the night into early Sun. Raised PoPs significantly for today into early Sun given strong lift Thermal profiles indicate p-type mainly liquid east of the Blue Ridge through the evening with colder air filtering and rain changing or mixing with snow by 12Z Sun. Have generally 1-2 inches of snow accumulation for the Potomac highlands which is short of an advzy.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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Precip endind by midday Sun with high pressure building in from the west. Turning cooler under decent CAA. High pres shifts south Mon afternoon with sct rain showers expected with next frontal passage. Cdfnt clears the area by 12Z Tue.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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Computer model guidance is in good agreement about the extended portion of the forecast. Aloft, troughing will persist through the middle of the week, giving way to a ridge by Friday. At the surface, a cold front will be settling south of the area Tuesday morning. A wave of low pressure will ride along the front Tuesday night, while a secondary front pushes south into the area by Wednesday morning. Canadian high pressure will then settle southeast, crossing the area Thursday and continuing offshore Friday. In terms of precipitation, the only notable chance comes with the Tuesday night low pressure. While there is some spread in QPF fields, the consensus at the moment has the best opportunity for the southern quarter of the forecast area. Deterministic runs suggest profiles will be warm enough for rain, but a few GEFS members crash in enough cold air with the secondary front for a changeover to snow before ending. At the moment, it doesn`t appear to be an impactful system regardless of p-type. The coldest period of the week will be Wednesday into Thursday behind the second cold front, with highs in the 40s to lower 50s and lows below freezing. The rest of the period will be fairly close to seasonal normals.
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&& .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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IFR cigs this morning as warm front lifts through, then MVFR today and tonight with ra/sn showers. Gusty N or NNW winds on Sunday. A period of sub-VFR conditions is possible in rain and low clouds, mainly at CHO, Tuesday into Tuesday night as low pressure moves south of the area. Otherwise VFR prevails through Wednesday. NW winds could gust to 20 kt both Tuesday and Wednesday.
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&& .MARINE...
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Winds will diminish later this morning and remain below SCA through early this evening. Winds strengthen tonight with solid SCA conditions expected. Winds will begin to gradually diminish Sun night but remain at aoa SCA into Monday. After a cold front pushes south, NW flow will dominate Tuesday into Wednesday, although it could become NE-N for a period as low pressure passes to the south Tuesday night. SCA conditions will be possible both days.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 11 PM this evening to 6 PM EDT Sunday for ANZ530>543.
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&& $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...ADS AVIATION...ADS/LFR MARINE...ADS/LFR

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