Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201835 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 235 PM EDT Tue Sep 20 2016 .SYNOPSIS...
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High pressure will build over the region through Thursday. A cold front will move through the area early Saturday. High pressure builds again over the region early next week.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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High pressure will build over the region tonight through Thu leading to drying and clearing skies. Main challenge next 24 hrs is whether fog will form overnight or not. NSSL WRF-ARW simulated cloud imagery which performed really well last night does not show any low clouds or fog development for tonight. However, model soundings show a very shallow moist layer near ground with subsidence just above it, a pattern conducive to fog formation. However, gusty winds just above the inversion could result in dry air mixing down preventing fog from developing or just light fog. Thinking is that the northern Shenandoah valley (Martinsburg area) will be the most prone to dense fog overnight with just light 3-5SM mist elsewhere. Otherwise, just another fine day with temps in the low to mid 80s.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
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Fog appears less likely Wed night as models show sfc dewpoints dropping Wed night. High pressure will continue to hold over the area with fair weather conditions.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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Main weather story during the long term will be first real taste of autumn...as a cold front drops southward through the area Saturday. Friday into Saturday: Remaining warm prior to frontal passage, with highs 5-10 F above climatological normals. Dewpoints in the 60s will be just high enough for at least a hint of humidity. Moisture- starved cold front moves through the area during the day Saturday...with only a limited chance of precipitation (anything that manages to develop would be light and isolated). Sunday through Monday: Pleasant weather expected behind the front as high pressure builds into the area and dewpoints fall into the U40s/L50s. Temperatures also cool to near seasonable values with highs generally in the 70s and lows in the 50s/60s. Dry weather expected during this time. Tuesday: Next front approaches the region Tuesday. Quality moisture appears to be lacking again...so currently expecting limited precipitation chances.
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&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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Another difficult aviation forecast again for tonight. MOS guidance is not particularly too aggressive tonight in fog development as it was last night and even the more typical pessimistic LAMP guidance is not that aggressive either. Thinking is that KMRB will be the most prone to dense fog overnight with patchy light fog rest of the TAFs except VFR at KDCA. VFR conditions expected Friday through the weekend as a mostly dry cold front passes through the area. Winds shift from southerly to northerly with frontal passage Saturday into Sunday.
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&& .MARINE...
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Very marginal SCA conditions tonight through Wed on the lower Potomac and Chesapeake Bay. Right now, I`m on the fence whether to issue any SCA. Will decide here in the next hour or so. Winds forecast to remain below SCA values Friday. Winds could increase near SCA values near/behind cold front Saturday into Sunday.
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&& .TIDES/COASTAL FLOODING...
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Possible minor coastal flooding at Annapolis this evening. Confidence is low, so will not issue any CFW at this time.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...MSE AVIATION...MSE/LFR MARINE...MSE/LFR TIDES/COASTAL FLOODING...LFR

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