Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 270759 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 359 AM EDT Tue Jun 27 2017 .SYNOPSIS...
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A weak level trough will move track north of the region today. High pressure builds over the area Wednesday before moving offshore Thursday. Warm conditions expected towards the end of the week and through the weekend.
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&& .NEAR TERM /TODAY/...
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As of 3am, an upper trough rounds the Great Lakes (with the axis from MI to St. Louis) per water vapor imagery. A 1021mb surface high is centered over the central Great Plains. This surface high will continue to drift east in the wake of the upper trough axis to the central Mid-Atlantic through tonight. The high center will move off the mouth of the Chesapeake Bay Wednesday. West flow and cold air advection under the upper trough will keep temperatures below normal through Wednesday night. A weak cold front which switched the wind direction from SW to NW is still moving SE across St. Marys county and will clear the MD portion of the Chesapeake Bay by 5am. A line of showers and thunderstorms developed over the northern Chesapeake Bay as the trough crossed those warm waters earlier tonight. A similar phenomenon is possible this evening as another cold front (this one under the upper trough axis) pushes east through the area. The northern Potomac Highlands will see light to locally moderate showers move east across the area through 7am. These should generally dissipate as they encounter downsloping east of the Allegheny Front. However, this activity is riding potential vorticity advection ahead of the upper trough axis and the early diurnal heating this time of year should enable redevelopment east of the Blue Ridge per high resolution guidance. Maintained low chance PoPs east of the Blue Ridge for this afternoon when a second round of precip is likely given the approach of the upper trough axis and peak heating. Max temps raised to low 80s today as 11C 850mb temps mix down in westerly flow.
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&& .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/...
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The surface high pressure center crosses the LWX CWA Wednesday morning. Return southerly flow develops Wednesday afternoon with a gradual return to summerlike conditions. Pressure gradient looks light enough for good radiational cooling Wednesday night. Max temps around 90F on Thursday with dewpoints rising into the 60s.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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High pressure will have moved well offshore by Friday. This will allow warmth/humidity to stream into the Mid Atlantic. Upper level ridge will not bring the east coast especially high heights so expect to see highs around end-of-June climo norms of near 90. Low pressure is expected to spin over Ontario/Quebec this weekend. This will allow a weak cold front/trough to be in the vicinity of the Mid Atlantic which could provide a focus for shower/thunderstorm activity, although by no means should the weekend be a washout. Looking out to the 4th of July - there are differences between the Euro and GFS. One thing seems certain is that the possibility of it being an extremely hot day does not look to be in the cards. Euro shows east coast "in between short waves" while GFS has a short wave approaching the Appalachians Tuesay night. We have a chance of showers/thunderstorms in the forecast but we`ll continue to monitor in the coming days.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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VFR prevails through the week as high pressure slowly builds from the west. Passing shower/isolated thunderstorm both this morning and later this afternoon across the DC metros ahead of a cold front. High pressure overhead Wednesday with return southerly flow into the weekend. Majority of Friday/Saturday should be VFR. There will be potential for showers/thunderstorms - especially Saturday, which could drop conditions briefly below VFR.
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&& .MARINE...
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Weak cold front will continue moving SE through southern MD Bay waters through sunrise with Wly/NWly flow through tonight as surface high pressure slowly builds. Return southerly flow begins Wednesday night as the high shifts to Bermuda. Winds expected to be below SCA values Friday/Saturday. Showers/isolated thunderstoms will be possible on the waters Saturday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 4 AM EDT early this morning for ANZ533-534-537-540-541-543.
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&& $$ PRODCUTS...BAJ/WOODY!

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