Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191556 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1056 AM EST Sun Nov 19 2017 .SYNOPSIS... A strong cold front is moving off to the east today and high pressure will build to our south tonight through Monday night. The high will move offshore Tuesday and a cold front will pass through Tuesday night into Wednesday. Canadian high pressure will build overhead later Wednesday through Thanksgiving Day. Coastal low pressure will likely move well out to sea Friday and a cold front will pass through Saturday. && .NEAR TERM /THROUGH TONIGHT/... Deepening low pressure center over the St. Lawrence Valley will track northeastward through the day reaching eastern Quebec by tonight. Rain showers have changed to snow showers along and west of the Allegheny Front as cold air rushed behind the cold front, and upslope snow showers will persist through the day and into tonight. The intensity and coverage of the upslope snow showers will vary through the day, with the first heavy surge now over, followed by a second surge between 4 PM and Midnight tonight as a potent upper level shortwave crosses the region and moisture deepens again. A Winter Weather Advisory remains in effect for western Grant and western Pendleton Counties for 3-6" of snow. The other main story for today will be gusty west/northwest winds. As of this writing, it looks as though the best winds were just after the cold frontal passage during the pressure surge, and winds during the mid-late morning so far have been lackluster by comparison. May take down advisory within the next hour or so as winds are still expected to lessen further during the afternoon and evening hours. Temperatures today are not following the usual diurnal curve, remaining steady or rising slightly through the daylight hours. While climo day highs across the region are in the high 50s and low 60s, the after sunrise highs should range in the 40s/50s, locally near 60F south/east and in the 30s in the higher elevations. A potent upper level shortwave and secondary cold front will then cross the region late today into tonight. While passage should be mainly dry, enough moisture and even a small amount of instability may get picked up ahead of the front for a few flurries/snow showers to make it downwind of the mountain chain and into northwestern VA, the eastern panhandle of WV, and into central/northern MD. Lows tonight in the 20s/30s. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... High pressure will build south of the region on Monday leading to fair skies and dry weather. West/northwest winds in the morning will lessen and turn southerly by days end. Highs Monday within a few degrees of 50F. Warm air advection and southwest flow returns for Monday night and Tuesday ahead of the next northern stream shortwave. Uneventful weather expected during this time with lows Monday night in the 20s/30s and highs Tuesday warming back up through the 50s and approaching 60F. The shortwave is progged to cross the region Tuesday night with the potential for some showers. As southern stream energy also moves through the southeastern US, cyclogenesis does look to take place off the coast of the Carolinas, but looks to stay mainly S/E of the region at this point. As several models are showing showers from this coastal system reaching back towards I-95, did increase pops across the southeastern portion of the CWA. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... A cold front will move off to our south Wednesday while Canadian high pressure approaches from the north and west. The high will build overhead Wednesday night through Thanksgiving Day...bringing dry and chilly conditions. Shortwave energy in the southern branch of the jetstream will cause low pressure to develop over the Gulf of Mexico toward Florida Thanksgiving Day. The low is expected to track north and east...but latest guidance continues to suggest that it will be far enough out to sea so it has no impact on our weather. Will continue to monitor trends in guidance over the next few days. A northwest shift would have a significant impact on the forecast for Friday. As of now...it appears that a return flow around a departing surface high will bring somewhat milder conditions along with some sunshine. A cold front will approach Friday night before passing through Saturday. Blustery and much colder conditions are expected behind the cold front later Saturday and Sunday. Upslope snow showers are possible along/west of the Allegheny Front. A few flurries could even spill east of the mountains but confidence is low at this time. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/... Main aviation weather concern through today will be gusty west to northwesterly winds. West/northwest winds have been gusting 30-40 knots, but will gradually lessen during the afternoon hours. Otherwise, mainly VFR is expected through Tuesday. The next chance of any precipitation and possible restrictions will come Tuesday night with the next system. High pressure will bring VFR conditions Wednesday through Thanksgiving Day. Coastal low pressure is expected to move out to sea Friday so more VFR conditions are likely. However...the track of this low will have to be monitored closely. && .MARINE... A Gale Warning remains in effect through today for all waters. Gusty west/northwest winds with gusts to 30-40 knots will gradually lessen during the afternoon hours. Small Craft Advisories are then in place for tonight and into Monday as northwest winds gradually abate. Sub-SCA winds are then expected Monday night, before the next chance for SCA winds arrive on Tuesday/Tuesday night ahead of the next system. High pressure will build overhead Wednesday through Thanksgiving Day. A Small Craft Advisory may be needed for portions of the waters Wednesday into Wednesday night. Still watching for the potential of a coastal low Friday. As of now...it appears that the track will be well out to sea so the most likely scenario is for it to not have any impact. && .TIDES/COASTAL FLOODING... Strong offshore flow behind the front is causing anomalies to sharply fall through this afternoon. Tidal blowout conditions are possible tonight. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Wind Advisory until 3 PM EST this afternoon for DCZ001. MD...Wind Advisory until 3 PM EST this afternoon for MDZ003>006-011- 013-014-016>018-501>508. VA...Wind Advisory until 3 PM EST this afternoon for VAZ025>031-040- 052>054-501-503>508. WV...Wind Advisory until 3 PM EST this afternoon for WVZ050>053-055- 501>506. Winter Weather Advisory until 11 PM EST this evening for WVZ501-505. MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EST Monday for ANZ530>534-537>543. Gale Warning until 6 PM EST this evening for ANZ530>543. Small Craft Advisory from 6 PM this evening to 10 AM EST Monday for ANZ535-536. && $$ SYNOPSIS...BJL/RCM NEAR TERM...MM/RCM SHORT TERM...MM/RCM LONG TERM...BJL AVIATION...BJL/MM/RCM MARINE...BJL/MM/RCM TIDES/COASTAL FLOODING...BJL/RCM

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