Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 271825 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 225 PM EDT Sat May 27 2023 .SYNOPSIS...
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Dry conditions look to continue through tonight with high pressure remaining north of the region. High pressure will slide offshore late tonight while coastal low pressure pushes northward from the Carolinas. Rain chances will increase Sunday and persists through at least Tuesday. High pressure builds back in by the middle part of next week with above average temperatures.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Dry conditions are expected through this evening. Plenty of sunshine across the area, though noticeably denser cirrostratus begins to fill in south of I-66 this afternoon/evening. There is so much dry air in the low to mid-levels of the atmosphere that any precip moving into the central VA Piedmont this evening is likely to be virga. Although, cannot rule out some drizzle or a very light shower.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
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An extratropical low east of the Savannah will steadily move north, moving inland along the Carolina coastline sometime over the next 12- 24 hours. This low is developing in a broad area of strong 1000- 925mb frontogenesis, and is also begin aided by a developing large cutoff low over the Southeast U.S. To the north, high pressure offshore of southern New England will become stretched out, though retain its influence across that region through Monday. The entire complex of the surface low, area of frontogenesis, and mid/upper cutoff low will meander over the southern Appalachians and Carolinas on Sunday, then shift toward coastal NC/VA late Sunday into Monday. Moisture slowly advects northward into our area over the next couple of days, however it is going to take some time to erode the large amounts of dry air currently in place. As a result, rain chances were reduced for most of the area Sunday, especially north of I-66 where it should remain mostly dry (though cannot rule out a stray shower or drizzle at times). The best rain chances are going to be Sunday evening through Monday night as the surface low moves into central NC/southern VA and the main area of frontogenesis lifts north into our area. Even then, the highest rain chances are going to be along/south of I-66, with much lower chances near the MD/PA border. Overall the rain looks to be light, with embedded moderate showers at times. A few thunderstorms are possible each afternoon, though the highest chance for that is also on Monday. Abundant cloud cover keeps afternoon temps below normal Sunday, with highs forecast in the mid 60s in central VA/central Shen. Valley to lower 70s along the MD/PA border. Temps a bit more uncertain for Memorial Day due to rain/cloud mix, though likely to also be below normal in the upper 60s to low 70s. Overnight lows in the 50s.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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The extended period will be a tale of two seasons with near normal to slightly below normal temperatures to start the period followed by early Summer heat to round out the workweek. Synoptically, the upper level pattern will remain fairly wavy/blocky with a broad closed upper level low weakening over the Carolinas drifting northeast into our region midweek. This will keep temperatures at or below average through at least Wednesday with periods of showers and even a few thunderstorms during the afternoon and evening hours. No washouts are expected between this period although considerable model spread as the low gradually fills and is nudged to the east with the trough flattening over Canada and a broad diffuse area of high pressure aloft building southward over the eastern U.S. This will lend to a reduction in precipitation chances each day starting with Tuesday afternoon and continuing into the end of the workweek. By Thursday and Friday, temperatures will trend upward while precipitation chances continue to decrease. Once again, this will be highly dependent on weakening low pressure kicking offshore and the strength of high pressure building aloft. Although model guidance differs consensus suggests that the high pressure system will win out yielding warm and muggy conditions across the region. Temperatures will head back above average Thursday and Friday with highs approaching 90 degrees. Precipitation chances remain low, but are not zero with a focus over the mountains and along the bay during the afternoon and early evening hours. With the high nearby overall forcing remains subtle at best, but something to watch with some of the modeling continuing to drop a backdoor cold front into the region Friday into Saturday. The front would further enhance convection although 12z guidance suggests a FROPA beyond peak heating time period late Friday into Saturday. Forecast confidence in the long term periods remains moderate due to large model spread for both precipitation chances and temperatures within the mid and late week period.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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VFR conditions are expected through tonight, with only increasing high-level cirrus as low pressure over off the South Carolina coastline moves northward. Lower CIGs are expected to reach CHO late tonight, likely producing MVFR conditions with a low chance for IFR conditions. Dry air still in place along/north of I-66 is likely going to keep CIGs at VFR from IAD/DCA northward on Sunday. Scattered showers at CHO, with just light rain possible elsewhere for Sunday. The main period for more persistent rainfall and possible CIG/VSBY restrictions is going to be Sunday night into Monday evening as the remnants of the surface low over the Carolinas moves into southern VA. MVFR to IFR cigs along with periodic showers and thunderstorms will likely continue through Tuesday evening as closed low pressure drifts offshore. Sub-VFR conditions may linger into the first half of Wednesday although confidence remains low with low pressure moving offshore and high pressure building. Higher confidence for VFR conditions returning late week.
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&& .MARINE...
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Winds steadily increase through the afternoon as pressure gradient over the region increases, in response to a developing area of low pressure off the South Carolina coast and high pressure offshore of southern New England. Gusts up to 25-30KT will be possible in the lower bay, and around 20-25KT elsewhere. Winds diminish slightly overnight, likely falling below SCA criteria in parts of the northern bay and upper Tidal Potomac. A second surge in winds is forecast Sunday morning into afternoon. Winds fall below SCA criteria late Sunday night. The surface low over the Carolinas drifts north through the weekend, eventually reaching southern VA where it opens into a weak/broad trough. Winds are forecast to be just below SCA criteria, but it is possible some gusts up to 20KT occur in the lower bay Monday afternoon. SCA level winds will persists into Tuesday in northeast flow as cutoff low pressure gradually relinquishes it`s grip over the region. By Wednesday, the pressure gradient looks to relax, allowing for lighter winds still from the northeast direction. These conditions will likely continue into Thursday and Friday as high pressure builds from the north. Winds will switch to the south and southwest Thursday before turning to the south and southeast Friday.
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&& .TIDES/COASTAL FLOODING...
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Low tidal anomalies will keep tidal levels below Action Stage at all locations for the high tide cycle this afternoon. However, there are higher anomalies in the southern bay, which will move up the bay tonight as winds weaken. Sensitive locations are likely to reach Action Stage over the next 2-3 tide cycles, and tidal levels might near Minor Flood at DC Waterfront and Straits Point Sunday afternoon.
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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 2 PM EDT Sunday for ANZ530>532- 538>540. Small Craft Advisory until 8 PM EDT Sunday for ANZ533>537- 541>543.
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&& $$ SYNOPSIS...EST NEAR TERM...KRR SHORT TERM...KRR LONG TERM...EST AVIATION...KRR/EST MARINE...KRR/EST TIDES/COASTAL FLOODING...KRR

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