Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 180128 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 928 PM EDT Wed Aug 17 2016 .SYNOPSIS... A weak cold front will gradually move south of the area through Friday before dissipating. Another cold front will cross the area early next week. High pressure returns for the middle of next week. && .NEAR TERM /UNTIL 7 AM THURSDAY MORNING/...
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Activity as of the 9 PM hour is pretty much centered around two distinct cold-pool driven convective systems. Primary system which tracked across central Virginia now pushing through the I-95 corridor and will continue to push northeastward through the evening hours. Second system is moving in from the southwest towards King George County, the Potomac, and southern Maryland. Severe threat exists with these over the next 1-2 hours before gradually subsiding as they move northeastward and into a lower CAPE environment. Flash flood concern remains as well with multiple training thunderstorms, high rain rates, and high efficiency rain processes. Activity should diminish (at least to showers) by later tonight as the main wave/vort max moves to the east. Lows in the upper 60s to mid 70s.
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&& .SHORT TERM /7 AM THURSDAY MORNING THROUGH FRIDAY/... Deep moisture will shunt south of most of the area Thursday with WNW flow establishing. This will lead to slightly drier and cooler air. However, the washed out boundary will not be far away with potential for weak disturbances in the flow, so the best chance of a shower and storm will be across the south. Had to introduce POPs a little to the north on Friday, as there are some indications a wave could pass along the front to the south and result in a chance of showers and storms by afternoon or evening. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... High pressure will build to the north Friday night. Drier and slightly cooler, yet seasonable, air will funnel southward into our region. We can`t rule out a scattered shower Friday night due to a few week disturbances that may try to sneak under the building high pressure. Most of the activity will be across the Virginia Piedmont or lower Southern Maryland. The area of high pressure will weaken some over our region Saturday and Saturday night, allowing for additional weak disturbances to move in from the west and bring us a chance for additional showers or perhaps a thunderstorm. A moderate cold front is expected to move slowly eastward across the Great Lakes region Sunday. This front could spawn a few thunderstorms, mainly in the afternoon and along and west of the Blue Ridge Mountains. Showers and thunderstorms could linger Sunday night and Monday as the front moves toward the Chesapeake Bay and possible stalls just east of the bay. High pressure will build in behind the front Monday night and linger through Wednesday. Drier air and slightly cooler temperatures are expected. && .AVIATION /01Z THURSDAY THROUGH MONDAY/...
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Main aviation weather threat of strong to severe thunderstorms will continue through 04Z at DCA/BWI/MTN. Localized wind gusts up to about 40 knots and brief reductions to 1SM or less in heavy rain possible in the stronger thunderstorms. After 04Z, areas of showers will continue overnight. Conditions improve to mainly VFR. There may be areas of fog overnight as well, but coverage and density in question, so left out for now. A stray storm may cross near CHO both Thursday and Friday, but otherwise VFR should prevail. VFR conditions Friday night through Saturday night. Winds light and variable.
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&& .MARINE...
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Main threat will be thunderstorms and associated Special Marine Warnings for gusty/damaging winds through midnight. Winds after midnight generally westerly 5-15 knots. W to NW flow will continue through Friday, generally 10 kt or less. While a stray storm can`t be ruled out on southern waters, coverage will be much less than today. No marine hazards expected Friday night through Saturday night.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Flash Flood Watch until 3 AM EDT Thursday for DCZ001. MD...Flash Flood Watch until 3 AM EDT Thursday for MDZ011-013-014- 503>506. VA...Flash Flood Watch until 3 AM EDT Thursday for VAZ026>031- 038>040-050>054-501-502-505>507. WV...None. MARINE...None.
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&& $$ SYNOPSIS...ADS NEAR TERM...ADS/MM SHORT TERM...ADS LONG TERM...KLW AVIATION...ADS/MM/KLW MARINE...ADS/MM/KLW

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