Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251915 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 315 PM EDT Mon Jul 25 2016 .SYNOPSIS... A cold front will drift into the region from the north tonight. This front will stall across the region during the middle of the week. Another cold front is expected at the end of the week. && .NEAR TERM /THROUGH TONIGHT/... A cold front extends from western NY to the Ohio Valley this afternoon. Another confluence zone extends into the Appalachians. The hot and humid airmass across the Mid-Atlantic is supporting MLCAPE in excess of 2000 J/kg. Isolated storms are developing over the mountains, but more organized convection is developing in the better lift to the north. Hi-res guidance indicates the northern part of the area has the highest risk to see some of these organized storms during the early evening hours, particularly the Baltimore area. It`s possible the activity could be weakening though as it travels parallel to the low level shear vector. Locally damaging wind gusts will be the biggest threat. However, relatively slow storm motion and PWAT near 2 inches will support locally heavy rain. Flash flood guidance is over 2 inches/hour in much of the area though. Most of the evening storms should either dissipate or exit the are by midnight. However, as the boundary sinks southward, can`t rule out some rogue showers/storms lingering. Low temperatures will be in the 70s for most locations. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... The front will become stalled across Virginia, likely toward the southern half of the area, for Tuesday and Wednesday as it becomes parallel to the upper level flow. Thunderstorm chances will largely be diurnally based each day, but with the front in the area and potential for subtle shortwave troughs to be moving across the area, it will be tough to pinpoint any dry periods. For Tuesday afternoon, bulk shear will again be in the 25-30 kt range in the midst of strong destabilization over the southern portions of the forecast area, so a Marginal Risk of severe weather has been introduced. Wednesday afternoon and evening will need to be monitored as well as the pattern changes very little. High PWAT will mean heavy rain is also a threat. Temperatures will lower a little for the next two days, generally in the low to mid 90s. However, heat indices will approach 100 yet again, especially Tuesday, with the highest values over the far southern areas. Overnights will remain in the 70s. && .LONG TERM /THURSDAY THROUGH MONDAY/... Main story Thursday through the weekend will be persistent above normal temperatures (though not too extreme) and the potential for showers and thunderstorms (some of which could be heavy at times). Front will linger near the area Thursday, which will keep chances for at least isolated afternoon thunderstorms in the forecast. Mid 90s temperatures coupled with upper 60s dewpoints yields heat index values in the upper 90s Thursday. Heights begin to fall late Thursday as shortwave approaches. While timing differences exist among long term guidance, the best chance for precipitation will occur as this feature crosses the area late Thursday into Friday. Depending on the track, there could be some heavy rain across parts of the area. While uncertainty exists with next weekends forecast, general consensus is for above normal temperatures to continue, with at least isolated afternoon thunderstorm chances. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... Thunderstorms will be the main concern through the evening, particularly the 4-9 PM time frame. Heavy rain and strong wind gusts will be possible. With somewhat scattered coverage, have left as VCTS for now. Baltimore area may have a slightly better chance at seeing some organized storms. In the humid airmass, can`t rule out some fog, particularly where storms cross. Nearby frontal boundary will allow for isolated afternoon thunderstorms Thursday. Better chance for scattered showers/thunderstorms arrives late Thursday into Friday as upper level energy approaches. && .MARINE... Overall winds expected to be 10-15kts from the W or SW today and tonight. A brief surge of SW winds ahead of a cold front is possible across the southern Chesapeake Bay late tonight and will need to be monitored. Showers and thunderstorms will become increasingly possible by late afternoon/ early evening. Some storms may be strong to severe resulting in gusty winds. SMWs will be likely. A cold front will move through the waters Tuesday morning and winds will become W to NW behind it. Showers and thunderstorms are possible Tuesday afternoon mainly across the southern waters and again on Wednesday as the front stalls out. While gradient winds remain below SCA criteria through the end of the week, thunderstorms will be possible Thursday and Friday. The best chance for showers/storms is late Thursday into Friday as upper level energy approaches. && .CLIMATE... The last time we hit 100 degrees: DCA: July 26th 2012 (100) BWI: July 18th 2012 (104) DMH: July 19th 2013 (100) IAD: July 18th 2012 (101) CHO: July 8th 2012 (106) HGR: July 7th 2012 (101) MRB: July 7th 2012 (100) Record maximum temperatures for July 25th: DCA (DC area): 100 (1930) DCA only: 99 (2010, 1987) BWI (Baltimore area): 100 (2010) BWI only: 100 (2010) DMH: 100 (2010) IAD (Dulles area): 98 (2010) IAD only: 98 (2010) CHO: 101 (2010) HGR: 98 (2010) MRB: 101 (1933) DCA (DC area): 79 (1965) DCA only: 79 (1965) BWI (Baltimore area): 77 (1887, 1885) BWI only: 76 (2001, 1965) DMH: 78 (2011) IAD (Dulles area): 76 (1965) IAD only: 76 (1965) CHO: 74 (2010) HGR: 75 (2001) MRB: 73 (2010, 2001, 1989, 1979, 1965) "Area" denotes ThreadEx sites which are the numbers used for RERs. && .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 MDZ003>006-011- 013-014-016>018-503>508. VA...Heat Advisory until 8 PM EDT this evening for VAZ028-030-031- 036>040-050>057-501-502-505-506. WV...Heat Advisory until 8 PM EDT this evening for WVZ052-053. MARINE...None. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...MSE AVIATION...ADS/MSE MARINE...ADS/MSE CLIMATE...DFH is the U.S. government's official web portal to all federal, state and local government web resources and services.