Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200136 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 936 PM EDT Fri May 19 2017 .SYNOPSIS... A cold front will push south through the area tonight. The boundary will stall out to the south later Saturday. The boundary will return north as a warm front into our area late Sunday before a stronger cold front passes through from the west Monday. High pressure will briefly return for Tuesday before another cold front impacts the area Wednesday. && .NEAR TERM /THROUGH SATURDAY/...
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Scattered showers and isold t-storms still ongoing at this time mainly across ncntrl MD and nrn VA. With sfc cdfnt still north of the Mason-Dixon line and some instability left am forced to keep chance of showers through the rest of the night with an even slight chance of a t-storm. The chances are significantly lower south of I-66 where this area will be removed from strongest forcing.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... The front will stall south of the area Saturday, and possibly remain there well into Sunday. Onshore flow will develop, leading to cloudier and cooler conditions. Model guidance differs on the thickness of cloud cover and thus temperatures. Have high temperatures on either side of 70 both days, but it could be cooler if thick, low clouds develop. Precipitation chances will be limited for Saturday through Sunday morning. There is a better chance of showers across western parts of the area due to upslope and overrunning flow. Depending on the position of the warm sector, thunderstorms could also develop Saturday in Highland/Pendleton Counties. Should any of this activity try to move eastward, it will quickly weaken in the stable airmass. A low level jet will increase ahead of an approaching cold front Sunday afternoon into Sunday night. It`s uncertain how much the warm front lifts back north, but nevertheless, forcing and moisture will be there for increasing chances of rain, especially during the second half of Sunday night. There could be a rumble or two of thunder with elevated instability. && .LONG TERM /MONDAY THROUGH FRIDAY/... A cold front will move across the region Monday bringing increased chances of thunderstorms that could produce heavy downpours. Dry air returns with a separate area of high pressure building in from the west Monday night through Tuesday. A low pressure system over the lower Great Lakes will intensify as it meanders eastward Tuesday night through Wednesday night. There is a chance for showers and perhaps a thunderstorm or two as pieces of energy rotate around the main storm system. A breezy and dry day expected Thursday, mainly to the east of the Potomac Highlands, with high pressure building in from the west. A few rain showers are possible in the Potomac Highlands. A piece of upper level energy could bring a chance for a few showers Friday. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
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Sct showers and isold t-storms will remain possible overnight. Prob at any specific airport is too low to warrant any tempo groups. Better chance of showers appears to be at BWI. Onshore flow will develop Saturday through Sunday. The marine air will increase the chances for low clouds...especially later Saturday night and Sunday. Models differ on if MVFR clouds form Saturday, so have placed this possibility in a SCT group (except CHO where there is better agreement). More low clouds are likely Sunday night along with increasing chances for rain ahead of a cold front. IFR conditions possible at all terminals Monday. Winds southwest becoming northwest 10 knots. VFR conditions Monday night and Tuesday. Winds northwest 5 knots Monday night becoming southeast 5 knots Tuesday. MVFR conditions Tuesday night with a chance of showers. Winds south becoming west 5 to 10 knots.
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&& .MARINE...
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A cold front will pass through the waters late tonight. The pressure surge with the cold front will cause north to northeast winds behind the boundary to gust around 20 knots. A Small Craft Advisory is in effect for the waters later tonight into Saturday morning. Have extended the SCA into the afternoon for much of the Chesapeake Bay and lower Tidal Potomac, as the pressure gradient looks strong enough to keep winds elevated. Wind fields should decrease Saturday night. The onshore flow will continue through Sunday before turning southerly Sunday night ahead of an approaching cold front. A Small Craft Advisory may be needed for portions of the waters Sunday night. The front will cross the area Monday, with the gusty wind threat decreasing. Lighter winds Monday night through Tuesday night with high pressure.
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&& .TIDES/COASTAL FLOODING... Onshore flow will develop this weekend, turning southerly by Sunday night. Water levels will increase, with anomalies supporting a minor coastal flood threat at Annapolis and Straits Point by Sunday night. && .CLIMATE...
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No records were set today. Cooler wx tomorrow and into early next week.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EDT Saturday for ANZ531-539. Small Craft Advisory until 11 AM EDT Saturday for ANZ530-538. Small Craft Advisory from 1 AM to 6 PM EDT Saturday for ANZ532>534-536-537-540>543. Small Craft Advisory from 1 AM to 11 AM EDT Saturday for ANZ535.
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&& $$ SYNOPSIS...ADS NEAR TERM...LFR SHORT TERM...ADS LONG TERM...KLW AVIATION...ADS/KLW MARINE...ADS/KLW TIDES/COASTAL FLOODING... CLIMATE...

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