Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 281537 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1137 AM EDT Sun May 28 2017 .SYNOPSIS... A surface trough will move across the area tonight followed by a weak cold front Monday afternoon. Upper level low pressure will linger north of the Great Lakes Monday night through the remainder of the week with persistent weak high pressure over the Mid-Atlantic. && .NEAR TERM /THROUGH TONIGHT/... A flash flood watch has been raised for our western five counties (Potomac Highlands and Highland County) which goes from noon to 10pm. Mid-morning sunshine out there caused scattered showers with thunderstorms expected to develop this afternoon. Previous discussion... As of 10am, upper level low pressure is along the Manitoba/Ontario border with a surface trough extending south to Duluth. This low will drift east along the north shore of Lake Superior through Tuesday. The cold front with this low is currently over eastern Wisconsin. Low pressure will develop along this front as it moves over the lower peninsula of Michigan later today. This will help push the weakening trough south of this area to the central Appalachians. Concern for flash flooding is across the far northwest part of the CWA/invof Cumberland where surface convergence/lift will be strongest and a plume of 1.5+ inches of PW will advect in. 1-2 inch hourly rain rates can be expected with heaviest showers/thunderstorms. Isolated instances of flash flooding are possible mainly along the Allegheny Front where one hour flash flood guidance 0.75 to 1.0 inches. Think severe threat will be more limited due to plenty of cloud cover and weak instability below 1000 J/kg. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Things will calm down somewhat as drier air filters in on westerly flow, but it won`t be completely dry. Still risk of showers/t-storms Tue afternoon as a weak cdfnt moves through. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... The upper level pattern for the middle and end of the week will feature a closed low drifting across eastern Canada. While increasing model spread of this feature late in the week lends some uncertainty, there is some signal in the noise. On Wednesday, a weak cold front will be drifting south of the area. There are some indications this front could waver, resulting in lingering chances of showers, but eventually high pressure building from the west should lead to higher probabilities of dry conditions. Thursday has the highest probability of being dry this week. Return flow will begin on Friday, although forcing/instability aren`t that notable. A cold front will be sinking southward next weekend, although progress will be slow since it will be parallel to the upper flow. Thus an unsettled period appears probable, but timing is uncertain. Temperatures will settle close to normal behind the front on Wednesday and Thursday, then warm back up (highs in the 80s) ahead of the next front on Friday and Saturday. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/... IFR conds out west lift through rest of the morning. Showers and t-storms this afternoon and evening with brief MVFR/IFR cigs in t-storms with heavy rain, mainly west of DC metros. Overall Wednesday should be VFR, but there is a small chance of showers as a front sags south of the area. Winds could also gust around 20 kt. VFR conditions are expected Thursday as high pressure builds in from the west. && .MARINE... Southeast flow through tonight becomes NW late Monday as a weak cold front moves through. Winds expected to remain below SCA through the first half of the week, but higher winds and waves can be expected near thunderstorms. Depending on the position of a cold front, winds could near SCA levels on Wednesday but confidence is low. Lighter winds are expected on Thursday as high pressure builds in from the west. && .TIDES/COASTAL FLOODING... Water anomalies will continue to rise through 12Z Mon with minor coastal flooding expected at many sensitive sites. Winds turn westerly on Mon, but they will be generally light and may not be able to lower anomalies that much. Please pay attention to coastal flood advisories. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 2 PM EDT this afternoon for DCZ001. MD...Flash Flood Watch until 10 PM EDT this evening for MDZ501-502. Coastal Flood Advisory until 7 AM EDT Monday for MDZ017. VA...Flash Flood Watch until 10 PM EDT this evening for VAZ503-504. Coastal Flood Advisory until 2 PM EDT this afternoon for VAZ054. WV...Flash Flood Watch until 10 PM EDT this evening for WVZ501>506. MARINE...None. && $$ SYNOPSIS...BAJ/LFR NEAR TERM...BAJ/LFR SHORT TERM...LFR LONG TERM...ADS AVIATION...BAJ/ADS/LFR MARINE...BAJ/ADS/LFR TIDES/COASTAL FLOODING...LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.