Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210756 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 356 AM EDT Sun Aug 21 2016 .SYNOPSIS...
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A cold front over Ohio will move through the Mid-Atlantic this afternoon into the evening. High pressure then builds over the area into Tuesday before persisting offshore through the rest of the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Moisture will continue to increase this morning with showers expected to become more numerous after daybreak as a cdfnt extending from southwest Ontario swwd through Toledo and St. Louis moves ewd. Cdfnt will then enter the fcst area by late morning with widespread showers and scattered thunderstorms expected. Best chance of t-storms east of the Blue Ridge mtns based on HRRR 1-hr Max Lightning product. Storms may pose a threat of isolated damaging wind gusts due to fast storm motion of 20kt, moderate instability, and bulk shear values around 30kt. Rainfall amounts of half inch to inch and a quarter are expected from far northern VA to northeast MD which may result in isolated runoff issues particularly over the Baltimore metro area and northeast MD. WPC PQPF shows 10-40% chance of 0.5 inches in 6-hr with highest probs over far northeast MD. Overall, flash flood threat remains marginal attm due to fast storm motion of 20-kt and FFG of 2+in/6hr needed to bring streams to bankfull stage. Cdfnt exits the area quickly during the early evening with showers ending by 03z if not sooner.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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High pressure builds Mon and holds through Wed with temperatures returning to more typical values for late Aug.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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High pressure will begin to move off the Mid-Atlantic coast on Wednesday and Thursday, leading to a gradual warming trend to above normal temperatures. Most of the area should remain dry, although moisture return may allow for stray diurnal terrain convection on Thursday. A cold front is still projected to approach on Friday. Mid/upper level support is weak given a strong ridge over the SE CONUS. However, there may be enough low level convergence for at least some scattered showers and storms. ECMWF indicates highs may again exceed 90F ahead of the front. The front will begin to stall and weaken as it becomes parallel to the zonal flow around the SE ridge. However, 00Z guidance indicates Great Lakes high pressure will provide enough of a push for the front to drift south of the area on Saturday, resulting in little chance of rain. Thermal differences will be small on Saturday though, with temperatures remaining above normal.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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Widespread showers expected with scattered thunderstorms mainly BWI, DCA, IAD and MTN. Brief MVFR/IFR restrictions possible with t-storms. Cdfnt moves east of terminals by 00Z Mon with showers ending quickly and winds shifting to the NW. No significant weather expected Wednesday and Thursday as high pressure moves offshore.
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&& .MARINE...
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Widespread showers and scattered thunderstorms expected this afternoon into early evening may pose a threat of strong gusty winds which may require SMWs. Small craft advisory conditions expected late tonight through Mon afternoon with NW winds. High pressure then builds Mon through the middle of the week with winds gradually diminishing. Southerly flow of 5-10 kt expected Wednesday and Thursday as high pressure moves offshore. A cold front will approach Friday, and winds may increase slightly. Thunderstorms may accompany the front as well.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Monday for ANZ530>543.
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&& $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...ADS AVIATION...ADS/LFR MARINE...ADS/LFR

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