Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211759 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 159 PM EDT Fri Jul 21 2017 .SYNOPSIS...Weak upper level disturbances will be possible tonight through Sunday. An upper level trough of low pressure will move over the northeastern US early in the new week. && .NEAR TERM /THROUGH TONIGHT/... Showers and thunderstorms moving across the Appalachians will likely hold together as they move across the southern half of the fcst area. Thermodynamic profiles are very warm aloft (-3C @500 mb) and no svr warnings have been issued by offices to the west. T-storms will likely dissipate during the early evening. Otherwise, another very warm and muggy night similar to last night but with more cloud cover. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...Global and hi-res models continue to show an MCS forming over southern Wisconsin late tonight and moving across Chicago and eastern OH and wrn PA by Sat morning. While this complex is expected to weaken toward daybreak, redevelopment is expected during the afternoon across the local area. 0-6km shear increases somewhat supporting organized convection. CAPE is also on the increase given hotter temperatures and plenty of moisture (850 mb dewpoints of 15C). Some severe wx is possible, but ensemble guidance shows a large spread in CAPE values with some members showing only weak CAPE. Sunday appears to be shaping up a potentially more significant severe convective day. Models progged a stronger upper level disturbance with significant height falls for summertime standards. Shear is also on the increase and many ensemble members show moderate CAPE and some even high CAPE values over 3500 J/kg. Expect clusters of storms to move across the area some with damaging winds. && .LONG TERM /MONDAY THROUGH FRIDAY/... A cold front will approach the region Monday before pushing across the region Monday night. Showers and thunderstorms will develop along and ahead of this front. Highs will reach the 90s again. The front could stall just to our south Tuesday, allowing for a couple of showers or a thunderstorm to develop. High pressure will build in from the west and northwest Tuesday night through Thursday. Temperatures will be nearly 10 degrees cooler than previous days with a comfortable relative humidity. The next cold front will arrive and push across the region Thursday night and Friday. Another active pattern of showers and thunderstorms during the period and could linger into the weekend if the front stalls across portions of the region. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...Sct-bkn clouds tonight. A t-storm is possible at KCHO. Sct-nmrs t-storms more likely Sat and especially Sun. Mvfr to ifr conditions possible with showers and thunderstorms Monday and Monday night. Vfr conditions expected Tuesday. A shower cant be ruled out. Winds northwest becoming southwest 5 to 10 knots Monday and Monday night. Winds north 10 knots Tuesday, becoming northeast 5 to 10 knots Tuesday night. && .MARINE...Sct-nmrs t-storms Sat and Sun may require SMWs. No marine hazards expected Monday through Tuesday night. Winds southwest 5 to 10 knots Monday and Monday night. Winds becoming northwest 10 knots Tuesday, then northeast 5 to 10 knots Tuesday night. && .CLIMATE... Late July is climatologically the warmest time of the year, just like six months from now is the coldest time. How has the heat of 2017 compared with heat waves (up to now) in other years? I chose "consecutive days that reached 90 and above" as the criteria. At DCA there have been two times this summer with stretches of six consecutive days - beginning June 29 and again July 10. In terms of ranking (going back to 1871) these are #49 and 50. Currently DCA has exceeded 90 on four consecutive days. July 16 was 89, otherwise DCA would have exceeded 90 on eleven days in a row. For Baltimore there were also six consecutive days beginning June 29, which puts it in 37th place. Currently BWI has exceeded 90 on four consecutive days. July 16 was 89, otherwise BWI would have exceeded 90 on eleven days in a row. The all-time record for June-Aug: for Baltimore 25 consecutive days beginning 7/12/1995. For DC there have been two periods of 21 consecutive days - beginning 7/29/1988 and 7/25/1980. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory until 8 PM EDT this evening for DCZ001. MD...Heat Advisory until 8 PM EDT this evening for MDZ011-013-014- 016>018-504-506-508. VA...Heat Advisory until 8 PM EDT this evening for VAZ037>039- 050>057-502-506. WV...None. MARINE...None. && $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...KLW AVIATION...LFR/KLW MARINE...LFR/KLW CLIMATE...Woody! is the U.S. government's official web portal to all federal, state and local government web resources and services.