Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211919 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 219 PM EST Tue Feb 21 2017 .SYNOPSIS...
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High pressure will move off the east coast tonight. A weak disturbance will cross the area late tonight into Wednesday. High pressure will be located off the southeast coast of the United States late in the week. A cold front will pass through the area this weekend.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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High pressure will continue to move off the New England coast this afternoon. An onshore flow has allowed for cooler conditions compared to recent days...but still above climo. Climatologically highs should be in the upper 40s. We are still expecting highs this afternoon to be in the upper 50s...possibly lower 60s in the central Shenandoah Valley. A broken deck of high clouds will continue to move over the area as moisture sneaks in ahead of an upper-level disturbance. Partly to mostly cloudy skies are expected. A cutoff low in the southern stream of the jet will track through the Gulf Coast States tonight while an upper-level disturbance in the northern stream move into our area. The southern stream system should remain well off to our south...but there may be just enough moisture that makes it into our area for a few showers as the northern stream passes through. The best chance for showers will be overnight into Wednesday morning across central Virginia perhaps into southern Maryland. With less moisture farther north...the forecast remains dry for these areas although a few sprinkles cannot be ruled out. The upper-level disturbance will move off to the east by Wednesday and subsidence behind this system should allow for some sunshine. A southerly flow around high pressure over the Atlantic along with the sunshine will cause more unusually warm conditions. Leaned toward the higher guidance or even above based on temperatures aloft and mixing potential...but did tweak temps down a few degrees across central Virginia where cloud cover may hang on a bit longer. Max temps will be in the upper 60s to 70 degrees across most areas...but much cooler (50`s) along the shore of the Bay and along the ridge tops of the Potomac Highlands.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
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High pressure will remain over the Atlantic Wednesday night through Thursday night while upper-level ridging builds overhead. A southerly flow along with sunshine will result in unusually warm condtions for this time of year. Max temps Thursday are expected to be well into the 70s for most areas...but cooler (50s-60s) along the shore of the Bay and in the ridges. Near record warmth is possible during this time. See the climo section below. Very mild conditions are expected for both Wednesday night and Thursday night...but with increased moisture there will likely be areas of fog. Some fog may be locally dense. A couple popup showers are possible Thursday afternoon due to limited instability from daytime heating. However...coverage will be widely scattered or isolated and much of the time should be dry.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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Dry conditions expected for Friday with southerly flow over our region and high temperatures in the 60s and 70s. Deep low pressure moves across the Great Lakes and its associated cold front moves across the Mid-Atlantic on Saturday... showers and thunderstorms likely. Dry conditions return Sunday as high pressure builds behind the front. Shortwave trough could bring showers over our CWA on Sunday night, followed by dry conditions on Monday. Frontal boundary could increase PoPs again for Tuesday.
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&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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VFR conditions expected through this evening. Patchy fog is possible overnight...but coverage should be limited due to mid and high clouds along with low-level dry air still in place. A few showers are possible late tonight into Wednesday...mainly across KCHO. High pressure will build to our south and east for later Wednesday through Thursday night. Areas of fog are possible Wednesday night into Thursday and again Thursday night into Friday. Fog may be locally dense with IFR/subIFR conditions possible. Dry/VFR conditions expected for later Friday before a cold front approaches the area on Saturday... with showers and thunderstorms possible into Saturday. Sub-VFR conditions possible Friday night into Saturday at moments. Gusty winds expected Friday night into Sunday, reaching up to 20 kt.
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&& .MARINE...
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High pressure will remain off the coast through Thursday night. A southerly flow is expected during this time...but wind speeds should remain below SCA criteria. Dry conditions expected for Friday before a cold front moves across the Mid-Atlantic on Saturday. Showers and thunderstorms possible. Gusty winds expected Friday night into Sunday, with SCA conditions likely.
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&& .CLIMATE... Did a check to see how warm it has been both for meteorological winter and since Feb 1 at the three major airports in terms of ranking (average temp): The statistics below are from February 1st through February 20th. Since Dec 1 Since Feb 1 DCA 5th warmest 2nd warmest BWI 14th warmest 13th warmest IAD 2nd warmest 2nd warmest Unseasonably warm temperatures are expected during the second half of the week. Below are record daily high maximum and high minimum temperature values for the 22nd through 24th (Wednesday through Friday). February 22nd DCA 77 (1874) 60 (1874) BWI 74 (1874) 51 (1874) IAD 71 (1991) 52 (1981) February 23rd DCA 78 (1874) 51 (1922) BWI 78 (1874) 52 (1874) IAD 73 (1985) 51 (1975) February 24th DCA 78 (1985) 52 (1975) BWI 79 (1985) 55 (1985) IAD 79 (1985) 53 (1985) && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/IMR MARINE...BJL/IMR CLIMATE...Woody!

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