Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 290122 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 922 PM EDT Fri Jul 28 2017 .SYNOPSIS... Upper-level low pressure system will intensify as it moves over the Mid Atlantic tonight. This will slowly move east of the area Saturday before gradually moving away from the coast Saturday night into Monday. High pressure is expected to build overhead early in the week. && .NEAR TERM /THROUGH SATURDAY/...
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Upper low over ern OH continues to deepen per darkening on experimental GOES-16 water vapor imagery. Rain has picked up in intensity over western MD and ern WV panhandle with cooling cloud tops and lightning jump seen on Geostationary Lightning Mapper. Observed hourly rainfall rates with these showers have been around 1.5-1.75 inches per hour. These rains will pivot east overnight across ncntrl MD, cntrl MD, nrn VA and the Distric with a significant risk of flash flooding especially over areas that were hit hard earlier today. Trough axis will shift east of the area after 12Z Sat with rain diminishing in intensity.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... Surface low remains east of the area Saturday with TROWAL precipitation remaining over the area (some of which could be of moderate intensity) during the first part of the day. Soils expected to be saturated over much of the area...so while precipitation should be lighter in intensity...any additional precipitation could exacerbate hydro issues. Cloud cover and nearby precipitation will keep temperatures in the 60s to L70s Saturday. Drying out Saturday night through Sunday night as low moves far enough to our east keeping precipitation east of the area. Temperatures slightly below normal. && .LONG TERM /MONDAY THROUGH FRIDAY/... High pressure will be building across the Mid Atlantic for the beginning of next week, providing an extended period of tranquil weather. Return flow will return mid-week and showers/thunderstorms can not be ruled out mainly in the afternoon Wed-Fri week. A cold front may move south into the area Thu-Fri and provide another focus for showers/thunderstorms during this time. Temperatures will start the week mild-- almost cool-- for the last day of July, and gradually warm through the week. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... Low pressure will approach the terminals today before moving overhead and intensifying tonight. MVFR going to IFR later today. Widespread showers and thunderstorms are expected to develop with locally heavy rain and subsequent flight restrictions at times. Some storms may also contain gusty winds. More rain is likely Saturday as the low stalls out near the DelMarVa Peninsula. Gusty north to northeast winds are also possible during this time. Improving conditions Sunday as surface low shifts well east of the area. There is a low probability of flight restrictions Mon-Tue. && .MARINE... Low pressure will approach the waters today before strengthening overhead tonight. The low will likely stall out near the DelMarVa Peninsula Saturday through Saturday night. Gusty winds are possible with the low nearby...especially tonight through Saturday night. Small Craft Advisory in effect tonight through Saturday night for the Bay and for the 2/3 of the Tidal Potomac for the day Saturday. Gale force winds are possible Saturday afternoon/ evening...though probability of occurrence is currently too low for a warning. Northerly winds continue on the waters Mon-Tue. There is a low probability of SCA conditions through this time. && .HYDROLOGY... A Flash Flood Watch is in effect through Saturday afternoon for the northern 2/3 of the forecast area. Most likely rainfall amounts during this time will be around 2 to 4 inches (with locally higher amounts). This may cause instances of flash flooding. We have been in contact with EM`s in Montgomery and Prince Georges County - the large dams appear to be in good shape. Smaller dams/reservoirs will be more of a concern. && .TIDES/COASTAL FLOODING... It appears Sunday may be the next episode of coastal flooding on the Bay/Tidal Potomac. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Flash Flood Watch through Saturday afternoon for DCZ001. MD...Flash Flood Watch through Saturday afternoon for MDZ003>006- 011-013-014-016>018-501>508. Coastal Flood Advisory from 5 AM to 10 AM EDT Saturday for MDZ017. VA...Flash Flood Watch through Saturday afternoon for VAZ027>031- 038>040-050>057-501-502-505>507. WV...Flash Flood Watch through Saturday afternoon for WVZ050>053- 055-501>504. MARINE...Small Craft Advisory until 2 AM EDT Saturday for ANZ532>534- 536-537-540>543. Small Craft Advisory from 5 AM Saturday to 7 AM EDT Sunday for ANZ531>534-537-539>543. Small Craft Advisory from 10 AM to 7 PM EDT Saturday for ANZ530-535-536-538.
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&& $$ SYNOPSIS... NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE... HYDROLOGY... TIDES/COASTAL FLOODING...

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