Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 181327 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 927 AM EDT Sun Jun 18 2017 .SYNOPSIS... A very warm and humid air mass will remain in place through Monday until a cold front clears the area Monday night. Weak high pressure will build over the area for the middle of the week. && .NEAR TERM /THROUGH TONIGHT/...
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High pressure remains over the Atlantic while a cold front tracks through the Midwest. A southerly flow between these systems will usher in hot and humid conditions today. A bkn stratocu deck trapped underneath the nocturnal inversion for locations along and east of the Blue Ridge Mountains will continue to mix out late this morning. Increasing sunshine will cause max temps to range from the 70s and 80s in the mountains to the lower and middle 90s across most locations. The hottest conditions are expected along the Interstate 95 urban corridor...with heat and humidity causing heat indices around 100 to 105 degrees. Will continue with the heat advisory for Washington DC...Arlington County and the city of Alexandria as well as Falls Church. Heat indices are expected to be closer to 105 degrees due to the urban heat island. Will continue to watch for Baltimore...but confidence is a bit lower since low clouds may take a bit longer to mix out so temps may be a couple degrees cooler. The heat and humidity will lead to an unstable atmosphere this afternoon. NAM/GFS bufkit soundings are indicating around 1000-1500 J/KG of MLCAPE. However...there will not be much in the way of a lifting mechanism. Terrain circulation may be cancelled out by a strengthening low-level flow. Therefore...convection may have a tough time developing. Will continue with isolated to widely scattered showers and thunderstorms this afternoon since there will be little in the way of inhibition but any organized convection seems unlikely at this time due to the lack of a strong lifting mechanism. Any convection should dissipate around sunset due to the loss of daytime heating. However...additional showers and thunderstorms may propagate into western portions of the CWA overnight. Confidence is low due to the unfavorable timing...but with the warm and humid conditions overnight there will be some instability. Also...shear profiles will be strengthening as a cold front and its associated upper-level trough approach from the west. A few severe thunderstorms cannot be ruled out overnight...mainly west of the Blue Ridge Mountains but again confidence is low at this time.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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An upper level trough will be moving across the eastern Great Lks Mon pushing a cdfnt into the area. As cdfnt intercepts a plume of very high PWATs aoa 2.0 inches, expect widespread showers and t-storms to develop and last into the evening except in southern MD where they will likely last through much of the night. While shear will be on the increase through the day (0-6km values of 30-35kt) which would support organized convection, amount of instability available still remains questionable given thick clouds are likely to arrive early and there might be showers already by 12Z. 00Z EPS indicate probabilities of CAPE greater than 1000 J/kg well below 50%. While individual storm cell motion is progged at 30-35 kt, unidirectional wind profiles suggest some training/repeated convective activity is likely causing some concerns for flash flooding especially given the very high PWATs. Still believe the primary threat will be flash flooding and a flash flood watch may be required for the I-95 urban corridor of DC and Baltimore. Cdfnt clears the area late Mon night with showers ending in most areas except perhaps southern MD. Drier and more seasonable Tue-Tue night.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Low humidity but seasonable temperatures for Wednesday. A departing broad upper trough will allow for some potential for instability convection. By Thursday and Friday zonal flow will replace the trough. Surface features will be fairly benign...but given the low level flow, some amount of tropical moisture could make it up here from the Southeast during the late week. Next weekend looks to be our next cold front, although the timing of which day is uncertain given the model spread. Dewpoint temps and humidity are expected to increase day by day Wednesday thru Saturday. && .AVIATION /13Z SUNDAY THROUGH THURSDAY/...
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MVFR cigs should mix out late this morning. A popup shower or thunderstorm is possible this afternoon and early evening...but coverage will be isolated to widely scattered. Additional showers and thunderstorms are possible after midnight...but confidence remains low. Areas of low clouds are possible late tonight into Monday morning as well. A cold front will approach the terminals Monday before passing through Monday night. Showers and thunderstorms are possible. Thunderstorms may be severe...especially during the afternoon and evening hours across the eastern terminals. Weak high pressure may return for Tuesday behind the cold front...but a popup shower/thunderstorm cannot be ruled out. Other than possible showers and thunderstorms at times, no significant aviation concerns Wed through Fri.
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&& .MARINE... Solid SCA winds today through Mon under strengthening srly winds. T-storms on Monday may require special marine warnings. Winds begin to diminish late Mon night. Other than thunderstorms, no significant marine concerns Wed through Fri. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Heat Advisory until 6 PM EDT this evening for DCZ001. MD...None. VA...Heat Advisory until 6 PM EDT this evening for VAZ054. WV...None. MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ530>543.
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&& $$ SYNOPSIS...LFR NEAR TERM...BJL/LFR SHORT TERM...LFR LONG TERM...CAS AVIATION...BJL/CAS/LFR MARINE...BJL/CAS/LFR

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