Area Forecast Discussion
Issued by NWS Sterling, VA

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322 FXUS61 KLWX 231836 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 236 PM EDT Tue Aug 23 2016 .SYNOPSIS... High pressure remains over the region through much of the week with a cold front moving through on Friday. High pressure returns for the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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Even though high pressure is resting atop forecast area this afternoon, residual low level moisture has allowed for a decent cumulus field to blossom. Virginia and West Virginia are more affected than Maryland. Think that increased subsidence and then nocturnal cooling will permit a decrease during the mid-late afternoon hours. Therefore, will not forecast these clouds entering Maryland. Otherwise, there is not much to discuss from a synoptic standpoint. Mean layer RH less than it was last night/this morning. Believe there will be mostly clear skies, so radiational cooling will be a bigger driver. That is reflected in low temperature forecast. Since dewpoints still low, fog should be limited to patches in typical mountain valleys.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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Surface high pressure will slowly be working offshore Wednesday and Thursday. As a result, we should embark upon a warming trend. Upper 80s/near 90 for high temps seem likely again by Thursday. Dewpoints will start to creep upward too, but still at tolerable levels (lower 60s Tue, mid 60s Wed). As humidity increases, instability levels will rise as well on the back side of the ridge. NAM continues to place more emphasis on the westerlies across the northern half of the country. Consequently, more shortwave advection would be affecting area based on this solution, primarily Wednesday night and Thursday. GFS is far more reserved, and seems to be the more plausible scenario. Am keeping all areas dry Wednesday and Wednesday night, but with added clouds in the mountains. Although temps will be a little bit warmer, do not believe there will be adequate forcing for thunderstorms to develop. By Thursday, believe there will be a ribbon of instability, confined mainly west of the Blue Ridge. Going forecast has 30-40% chance of showers/thunderstorms in this area, which should address threat well.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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A weak cool front is expected to stall across the region Friday and Friday night. A spotty shower cannot be ruled out along the boundary. Temperatures will be on the warm side too with highs reaching the lower to middle 90s. High pressure will build in behind the front Saturday and Saturday night. Drier and cooler air expected. Temperatures will be closer to normal. This high will move east and weaken Sunday and Sunday night. Dry conditions will prevail Sunday. We can`t rule out a shower or thunderstorm in the west Sunday night as the next cold front moves across the lower Great Lakes. Temperatures remaining near normal. The cold front will move across the region Monday and Monday night. A chance of showers and thunderstorms will ensue through the period. Temperatures normal.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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There is a vigorous cu field across Virginia and West Virginia this afternoon, with bases (some cigs) 050-060. Believe this will erode prior to sunset. VFR through the evening. There may be some patchy fog overnight, but air mass quite dry...so am doubting how widespread it will be. Have limited MVFR to climo- preferred locations. VFR conditions should generally prevail Wednesday and Thursday as high pressure departs. Fog may be a little more pervasive by Thursday with added humidity. In addition, a few thunderstorms would be possible in the afternoon and evening, especially near MRB. VFR conditions expected Friday through Friday night. A brief period of MVFR or IFR is possible in any isolated thunderstorms near CHO, MRB, and IAD...mainly Friday evening. Winds southwest around 5 knots Thursday night becoming northwest around 5 knots Friday and Friday night.
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&& .MARINE...
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Winds light and variable over the waters this afternoon as high pressure is overhead. flow will become southerly over the next couple of days as the high pulls offshore. For the most part winds will be 10 kt or less. However, may have some gusts up to 15 kt due to channeling Wed and Thu nights.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...HTS SHORT TERM...HTS LONG TERM...KLW AVIATION...HTS/KLW MARINE...HTS/KLW

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