Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190800 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EDT Mon Jun 19 2017 .SYNOPSIS...A cold front will cross the area this afternoon with widespread showers and thunderstorms some with damaging winds and heavy rainfall. Weak high pressure will build over the area for the middle of the week. && .NEAR TERM /THROUGH TONIGHT/...Cdfnt currently approaching the Appalachians mountains will move into the fcst area later this afternoon and intercept a plume of exceptionally high PWATs (values greater than 2.0 inches). Model guidance show good sfc convergence setting up over the urban corridor, 12-hr height falls in the order of 30 meters, and upper level divergence on right entrance of a 100-kt jet streak on east side of upper level trough over Pennsylvania. This will encourage heavy precip rates this afternoon and early this evening. There are some competing factors that could temper the flash flooding threat. First, is the dry antecedent conditions of the past two weeks and relative fast progression/movement of frontal zone and fcst individual storm cell motion of around 35 kt. On the other hand, unidirectional wind profiles indicate potential for training convection while exceptionally high PWATS, very high 850 ThetaE values and K indices will support intense rainfall rates capable of producing 2-4 inches of rain in a short period of time. Have issued a flash flood watch where models and their respective ensemble means show the highest rainfall totals. The strengthening shear/wind fields and fast storm motion also indicate potential for damaging winds and SPC has parts of the area under an enhanced risk of severe wx. Cdfnt will clear the area during the mid to late evening hours with showers ending by midnight in most areas. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...Weak high pressure will build over the area supporting dry conditions and seasonable temperatures. && .LONG TERM /THURSDAY THROUGH SUNDAY/... The end of the week will feature quasi-zonal flow aloft across the eastern CONUS with the main jet stream to the north and subtropical ridge to the south. Thursday is the favored day to be dry during the extended period as weak ridging sits atop the area. It will likely also be the warmest day of the period. Two features will come into play for Friday into the weekend. First, low pressure (possibly tropical in nature) will have moved into the Gulf Coast states. There will also be low pressure near Hudson Bay, with a cold front gradually sinking southward. Model spread is high on the handling both of these features, though it looks like the weather will become increasingly unsettled heading into the weekend whether or not tropical moisture is pulled into the frontal zone. The front will likely stall near the area Saturday before wavering Sunday. A deeper upper level trough may approach by late Sunday. With the clouds and precipitation around, diurnal ranges will become muted, with low temperatures above normal and high temperatures near or below normal through the weekend. && .AVIATION /08Z MONDAY THROUGH FRIDAY/...Widespread showers and t-storms this afternoon into early evening with potential for damaging winds and heavy rainfall with brief 2-4 hrs of IFR/LIFR conditions. VFR conditions expected a few hrs after frontal passage tonight. VFR conditions likely Thursday. Thunderstorm chances will begin to increase on Friday. && .MARINE...Gusty winds through this evening with solid SCA conditions. T-storms will likely require special marine warnings at some point during the afternoon and evening. Winds diminish overnight tonight. SCAs possible again Tue into Wed night. Light winds with high pressure are expected Thursday. There is low confidence on the pressure pattern heading into Friday, but there is at least a chance of SCA conditions developing as early as Thursday night. Thunderstorm chances will also increase on Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Flash Flood Watch from 3 PM EDT this afternoon through this evening for DCZ001. Coastal Flood Advisory until 6 AM EDT early this morning for DCZ001. MD...Flash Flood Watch from 3 PM EDT this afternoon through this evening for MDZ005-006-011-013-014-503>508. VA...Flash Flood Watch from 3 PM EDT this afternoon through this evening for VAZ052>054-506. WV...None. MARINE...Small Craft Advisory until 9 PM EDT this evening for ANZ530- 531-535-536-538-539-542. Small Craft Advisory until 6 AM EDT Tuesday for ANZ532>534-537- 540-541-543. && $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...ADS AVIATION...ADS/LFR MARINE...ADS/LFR is the U.S. government's official web portal to all federal, state and local government web resources and services.