Area Forecast Discussion
Issued by NWS Sterling, VA

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270 FXUS61 KLWX 251427 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1027 AM EDT Sat Mar 25 2017 .SYNOPSIS... High pressure over the western Atlantic will be in control today. A back door cold front will drop southwestward into the area later tonight and Sunday. The front will lift back to the north on Monday. Another cold front will drop back south across the region later Tuesday or Tuesday night. The front will stall to the south of our area through the rest of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Plenty of cirrus this morning especially across the northern half. Clouds will thicken and lower during the afternoon as moisture continues to advect from the west southwest. Chance of showers increase during the afternoon as frontal zone across Pennsylvania pushes south. Lowered PoPs for the afternoon across the north and removed PoPs for remainder of this morning. Temps already in the mid 60s headed well into the 70s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... Confidence in a backdoor front and subsequent onshore flow/cold air damming has increased, so temperatures were lowered below guidance consensus particularly around Baltimore where low 50s are currently expected. Also, patchy drizzle was added to the Sunday forecast generally Blue Ridge and east. A sharp gradient between warm southerly flow and cool easterly flow is expected over southern portions of the CWA. Subsequent shifts will need to focus on this for the MaxT forecast. Guidance shifts the CAD wedge north Sunday night. However, it is wise to hold onto an onshore flow and lower temperatures longer than guidance, so gradual improvement is given for Monday. Low pressure currently over Oklahoma will continue to drift northeast reaching the the Midwest tonight before dissipating over the Great Lakes under a northern stream ridge Sunday night. A second low currently along the California coast will reach the Midwest Monday night before reaching the eastern Great Lakes Tuesday (and also dissipating) per 00Z ECMWF/GFS. Continued moist southwesterly flow warrants high chance PoPs with slight chance for thunder for the LWX CWA Monday. Possibly a break in action, so Monday night was kept low at this time. && .LONG TERM /TUESDAY THROUGH FRIDAY/...
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Guidance is not in great agreement regarding the weather systems in our region through the long term. However, most models agree that we will start out in the warm sector on Tuesday. Tuesday morning, the GFS has low pressure near Lake Erie, while the EC has the low further southwest over southern Indiana. GFS sends the low east across the St. Lawrence Valley and brings a cold front south in the evening, while the EC solution is slower and weaker with the low, with any frontal passage delayed until at least early Wednesday. This system will bring a threat of showers and thunderstorms with, with notable instablity progged across our region in the warm sector. By late Wednesday, both models have the front south of, with high pressure from Canada pushing cooler and drier air into the region. The remainder of the week appears to be in the cool sector north of the front. While Thursday starts out dry, by day`s end models bring another low pressure wave eastward into the region, with an increasing risk of rain by Thursday night and Friday. This system appears less likely to bring any thunder with it as current guidance generally keeps the warm sector away from us, resulting in a cool and rainy end of March.
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&& .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... VFR under high pressure and southerly flow through today. Backdoor cold front shifts west across the DC metros tonight with onshore flow 10 to 15 knots through Sunday. Drizzle and IFR conds eventually develop and spread east to west late tonight through Sunday. Southwesterly flow from low pressure to the west/north Monday brings rain showers to the DC metros Monday. Thunderstorms are the main concern Tuesday. This concern will end at night and Wednesday looks VFR with some gusty NW winds likely behind a cold front. && .MARINE... Southerly flow 10 to 15 knots today interrupted by a backdoor cold front tonight. Onshore flow expected Sunday into Monday before shifting south. Generally sub-SCA SWly flow prevails Monday. Thunderstorms are possible Tuesday. SCA possible behind a cold front Wednesday. && .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 9 PM EDT Sunday for ANZ530>532-538>540.
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&& $$ SYNOPSIS...RCM NEAR TERM...LFR SHORT TERM...BAJ LONG TERM...RCM AVIATION...BAJ/RCM MARINE...BAJ/RCM

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