Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191420 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1020 AM EDT Wed Jul 19 2017 .SYNOPSIS... High pressure will build into the region today and Thursday, followed by the potential for weak disturbances Friday and the weekend. An upper level trough of low pressure will move over the northeastern US to start the new week. && .NEAR TERM /THROUGH TONIGHT/...
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Upper level trough over the Carolinas has shifted considerably south and east of the local area this morning as compared to past few days putting local area under mid-upper level ridging. Experimental GOES-16 low-level water vapor 7.3 micron channel shows that dry air has spread a bit farther east today to near the I-95 corridor even though 12Z IAD sounding came in with higher PW values at 1.72 inches as compared to past two mornings. Hi-res models show considerable less convective activity today than past two days and this seems reasonable given trends seen in water vapor imagery. In addition, h5 temps have warmed up a deg or two C since yesterday which should tend to cap things off a bit. Still isolated t-storms are expected over the Blue Ridge mtns into northeast MD along the Chesapeake Bay due to orographic lift and sea breeze convergence respectively. Not anticipating any heat headlines today and are not likely tomorrow either. Heat headlines will probably be needed Fri and possibly Sat.
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&& .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... Building heat Thursday and Friday. High pressure centered over the M id-South states will direct organized thunderstorm development/MCSs from the Lake Erie area to the central Mid-Atlantic. Thursday night looks to be the first threat time for MCS activity. Heat advisory for portions of the area (mainly along the Bay shoreline and south of DC) Thursday with an advisory for most of the area likely Friday. 100F heat index criterion west of the Blue Ridge should allow greater advisory coverage than last year when the criterion was 105F out there. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Historically the latter part of July is the hottest period of the year in the Mid Atlantic, and this weekend will definitely fit that descriptor. Highs Saturday will be in the 90s over much of the area, with the cities reaching the upper 90s. With dewpoints around 70 this will push afternoon heat indicies of 100 to 105. Heat advisories will be likely. With this much heat/humidity in place afternoon/evening thunderstorms will be possible, especially over the mountains. "Sultry" will be a good decriptor for Saturday night. Lows generally in the 70s, possibly 80 in the cities. Sunday will be pretty much a repeat. A short wave moving into the Upper Great Lakes Sunday night may serve as an initiator for convection in the Ohio Valley. Whether or not this will be impact the Mid Atlantic remains to be seen. The worst of this heat wave should be put to rest Monday as the short wave tracks over New England. Temperatures will probably still reach 90 Monday. With the trof passing to the north there`ll be a chance for thunderstorms. Tuesday the trof will have moved off the coast, helping to bring the Mid Atlantic back to more "normal" temperatures with highs in the mid to upper 80s. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... VFR prevails under high pressure through the weekend. Organized thunderstorm chances Thursday night through the weekend. Saturday and Sunday VFR with the potential for showers and a few thunderstorms. Heavy downpours and gusty thunderstorms are possible in any storms. && .MARINE... Tranquil winds through the weekend, though organized thunderstorm chances begin Thursday night with high pressure centered over the Mid-South States. Winds expected to be below SCA values this weekend. Afternoon/evening thunderstorms will be possible each day. && .TIDES/COASTAL FLOODING... We are now at the higher of the two high tides and nowhere is in danger of reachng minor flood stage, hence there should be no problems with the daytime high tide cycle. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ Update...LFR Products...BAJ/WOODY! is the U.S. government's official web portal to all federal, state and local government web resources and services.