Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190845 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 345 AM EST Sun Nov 19 2017 .SYNOPSIS...
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A strong cold front will move 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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Deepening low pressure center near the east end of Lake Ontario early this morning will track northeastward through the day reaching eastern Quebec by tonight. An associated strong cold front is crossing the region as of this typing (330am) and it will be clearing east of the Chesapeake Bay by 7 AM. Widespread rain showers expected out ahead of the front, along with gusty south/southwest winds. As the front passes, expect a sharp turn to the west/northwest and surge in wind speed to the 40- 50 mph range. Rain showers will change to snow showers along and west of the Allegheny Front as cold air rushes 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 occurring between 4 AM and 10 AM, 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. Aside from gusts associated with frontal passage, the most widespread and strongest winds will occur just after sunrise (7am) through 12 noon or so when the best overlap of the wind field aloft and low level mixing occurs. Have maintained the Wind Advisory for much of the area aside from portions of central Virginia for gusts up to around 50 mph. Winds will lessen during the afternoon and evening hours. Temperatures today will not follow the usual diurnal curve with early morning mild temperatures falling after frontal passage, and then remaining steady or recovering slightly through the day. 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.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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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.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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Main aviation weather concern through today will be gusty west to northwesterly winds. South/southwest winds early this morning will turn sharply to the west/northwest following a frontal passage with gusts 30-40 knots expected this morning. Winds will gradually lessen during the afternoon hours. Along the front, a brief period of MVFR is also possible in low clouds and rain. 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.
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&& .MARINE...
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A Gale Warning remains in effect through today for all waters. Gusty south/southwest winds early this morning will turn sharply to the west/northwest following a frontal passage with gusts to 30-40 knots expected this morning, gradually lessening 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.
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&& .TIDES/COASTAL FLOODING...
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Water levels are around 1 to 1.5 feet above normal due to a strong southerly flow. These anomalies may creep up a bit before a cold front moves through between 5 am and 8 am. Will have to keep an eye out for Annapolis. Strong offshore flow behind the front will cause anomalies to sharply fall through this afternoon. Tidal blowout conditions are possible tonight.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Wind Advisory until 3 PM EST this afternoon for DCZ001. MD...Wind Advisory until 3 PM EST this afternoon for MDZ003-501-502. Wind Advisory until 3 PM EST this afternoon for MDZ004>006-011- 013-014-016>018-503>508. VA...Wind Advisory until 3 PM EST this afternoon for VAZ025>031-503- 504-507-508. Wind Advisory until 3 PM EST this afternoon for VAZ040-052>054- 501-505-506. 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...Gale Warning until 6 PM EST this evening for ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...MM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM MARINE...BJL/MM TIDES/COASTAL FLOODING...BJL

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