Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230901 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 401 AM EST Thu Feb 23 2017 .SYNOPSIS...
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High pressure will remain south of the area through Friday. A cold front will pass through the area on Saturday. High pressure builds over the area during the early part of next week. Another cold front will move through the area around the middle part of next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Light southeast flow and moisture advection has resulted in widespread stratus and areas of dense fog along the western shore of Baltimore and Harford counties. Short-term guidance suggests stratus layer will continue to expand next few hours with fog becoming an issue over northeast MD. Will continue to monitor obs for possible expansion of dense fog advisory. After low clouds/fog mix out later this morning, it will become very warm with highs reaching into the mid 70s. There will actually be sufficient instability (200-400 J/KG of CAPE) for pop-up scattered showers and isolated thunderstorms mainly between 20z-02z over the nrn Shenandoah valley, ern WV panhandle and north cntrl MD. Showers will dissipate with loss of heating later in the evening. More low clouds and/or fog tonight as area remains in warm sector.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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500 mb ridge crests over the area around 00Z Sat with sfc temps rising another 1-4F degs. An elevated mixed layer also advects northward into the area keeping atmosphere capped. Won`t rule a few spots hitting 80F. Very warm Fri night with record high minimums likely. Fog not likely to be a problem as winds strengthen, but low clouds still possible. Attention then turns to sharp cold front fcst to move through the area Sat. SPC DY3 Otlk now has entire area under marginal risk. Simulated cloud imagery from GFS shows convection remaining strong possibly severe as it moves across ern OH, wrn PA, and wrn MD between 12Z-15Z then weakening/becoming shallower after 15Z as it crosses the rest of the fcst area. Based on this, it appears any severe threat would be confined to morning hours as strongest forcing stays north over PA. Cdfnt clears the Chesapeake Bay by 00Z Sun, then turning much cooler and windy.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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High pressure will be building overhead on Sunday. While temperature departures will be some 15-20 degrees lower from Saturday, highs will still be near or slightly above normal. Outlying areas could fall below freezing Sunday night. The remainder of the extended period becomes much more uncertain. The upper level pattern will feature mean troughing in the western US and a building ridge over Florida and the Caribbean. With fast WSW flow aloft, any cold air intrusions are unlikely, with temperatures likely remaining above normal for the remainder of the forecast period. The tricky part will be timing in shortwave troughs within the fast flow, with the possibility of a front remaining somewhere near the area. If the GFS low pressure solution arrives early enough Monday, there could be a little wintry precipitation in the mountains, but this is far from certain. Otherwise, the forecast will carry a low chance of showers for each period due to the wide spread of model solutions. There is a little better agreement on more substantial troughing arriving late Wednesday or Thursday...which would represent a more targeted opportunity for rainfall.
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&& .AVIATION /09Z THURSDAY THROUGH MONDAY/...
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MVFR/IFR Cigs at KIAD, DCA, and BWI through 14Z then mixing out. Another repeat tonight with more low clouds. Sharp cdfnt to move through the area Sat with showers and gusty shifting winds. VFR with high pressure Sunday into Sunday night. There are a wide range of model solutions regarding the timing and strength of the next low pressure system arriving Monday (or later), thus confidence on impacts is low.
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&& .MARINE...
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Small craft advisory conditions likely Sat through Sun. Showers Sat afternoon may require SMWs. Winds will likely diminish through the day Sunday as high pressure moves into the area, but SCA conditions may continue for a time. The high will quickly move offshore Monday, but models differ on how strong southerly winds will become, depending on the strength of low pressure to the west. Will mention possible SCA conditions in the marine synopsis.
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&& .CLIMATE... Warmest Februaries (average temperature) DCA BWI IAD 1. 46.9 (1976) 44.0 (1976) 42.1 (1990) 2. 45.2 (1990) 43.9 (1949) 41.1 (1976) 3. 44.7 (1997) 43.3 (1890) 41.0 (1998) 4. 44.3 (2012) 42.7 (1932) 40.9 (2012) 5. 43.9 (1949) 42.6 (1909) 40.5 (1997) Feb 2017 (through the 21st) DCA: 45.1 BWI: 41.6 IAD: 42.1 Warmest Winters (Dec 1-Feb 28/29) DCA BWI IAD 1. 44.7 (1931-32) 45.3 (1931-32) 40.0 (2011-12) 2. 44.3 (1889-90) 44.4 (1889-90) 39.7 (2001-02) 3. 43.3 (2011-12) 42.4 (1948-49) 39.4 (1997-98) 4. 43.2 (2001-02) 41.9 (1949-50) 39.0 (2015-16) 5. 42.8 (1949-50) 41.3 (1879-80) 38.3 (1990-91) Winter 2016-17 (through Feb 21) DCA: 43.0 BWI: 39.6 IAD: 39.9 && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Dense Fog Advisory until 8 AM EST this morning for MDZ011-508. VA...None. WV...None. MARINE...None.
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&& $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...ADS AVIATION...ADS/LFR MARINE...ADS/LFR CLIMATE...DFH

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