Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 151906 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 306 PM EDT Tue Aug 15 2017 .SYNOPSIS...
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A weak disturbance will bring a chance for showers and a thunderstorm through this evening. An area of high pressure will build into the region later tonight through Wednesday night. A warm front will move northward Thursday into Thursday night followed by a cold front that should pass through the region later in the week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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As one batch of moderate to heavy rain and a few thunderstorms move east across the Chesapeake Bay and out of our area, a trough of low pressure will linger and bisect the region. Another upper level disturbance, moving eastward out of the eastern Ohio Valley and northeast Tennessee, could spark a couple of showers and a thunderstorm or two later this afternoon. CAPE still remains in the 1000 to 1500 J/kg range and precipitable waters remain near or above 2 inches. The main threats of any thunderstorms will be heavy rainfall that lead to localized flooding and occasional lightning. A gusty thunderstorm cannot be ruled out since our bulk wind shear is around 30 knots.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/...
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As the next upper disturbance moves east, so does the trough of support this evening. Most of any showers or thunderstorms should fade away or weaken around mid-evening with the loss of lift and, of course, daytime heating. High pressure will build into the region from the northwest overnight through Wednesday night. Generally light southeast winds this evening will become more northwesterly overnight and remain light. Expect some dry air to filter into the region overnight and Wednesday, but perhaps not enough dry air to prevent some patchy fog. As the high moves east Thursday, a warm front will develop across southwest Virginia and propagate northward. A chance of showers and a few thunderstorms is expected along and just north of the warm front, mainly Thursday afternoon. Temperatures are expected to climb into the upper 80s with dewpoint temperatures climbing into the lower to middle 70s.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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A cold front will be approaching our area on Friday with humid and warmer conditions ahead of it, which could lead to the development of showers and thunderstorms. The front will move across Friday night and stall near/south of our area Saturday into Sunday. This will continue to enhance the development of showers and thunderstorms through the weekend. There is uncertainty on the timing and as to how far south the front will stall. Uncertainty continues Monday into Tuesday as guidance suggests that upper level energy could enhance showers and thunderstorms, but other guidance is drier. High temperatures will be in the mid to upper 80s... 70s at higher elevations.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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VFR conditions expected to develop at all terminals later this afternoon and linger through the early hours of the overnight. We could have a brief period of MVFR conditions at some point this afternoon as additional showers and embedded thunderstorms develop, mainly near the CHO terminal. Otherwise, MVFR or perhaps IFR conditions could develop with patchy fog overnight at any one terminal, particularly where rain has fallen Tuesday. VFR conditions expected Wednesday through Thursday with a chance for showers or a thunderstorm Thursday afternoon. VFR conditions expected with periods of sub-VFR possible as showers and thunderstorms could develop Friday into Sunday with frontal boundary near by.
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&& .MARINE...
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No marine hazards expected later this afternoon through Thursday night. Winds light and southeast this afternoon becoming northwest 5 to 10 knots tonight and Wednesday. Winds becoming southeast 5 to 10 knots Wednesday night into Thursday. Mainly dry conditions expected with periods of showers and thunderstorms developing Friday into Sunday with frontal boundary near by. Wind gusts are expected to stay below the small craft advisory threshold.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...KLW NEAR TERM...KLW SHORT TERM...KLW LONG TERM...IMR AVIATION...IMR/KLW MARINE...IMR/KLW

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