Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230130 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 930 PM EDT Sat Apr 22 2017 .SYNOPSIS... A cold front will remain stalled to the south through Sunday. Low pressure will develop along the boundary...impacting our area through early next week. Low pressure will move out to sea Wednesday. A cold front may impact the area late in the week. && .NEAR TERM /THROUGH SUNDAY/...
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Cold front has pushed into North Carolina this evening. High pressure is centered over the Great Lakes and pushing east. Another low pressure is located to the south in Mississippi. Aloft, a trough of low pressure extends from Quebec southwestward to a closing-off low in southwest Missouri. The last of the rain is exiting southern Maryland. However, there`s another batch in southwestern Virginia. This should slide along the southern portion of the CWA during the middle of the night, with drier air winning the battle farther north. After this rain exits, there could be another break late tonight into early Sunday morning. Lower clouds have been clearing out of northern portions of the area, although the lower dew points are lagging in PA. With the thin clouds and rain-saturated conditions, there could be a little fog before drier air advects in (already seeing some reductions in visibility at MRB and OKV). Lows tonight will be in the 40s for most locations. During the day Sunday, it now appears that drier Canadian air will press southward far enough to dry us out. The northern half of the area may even see filtered sun through cirrus for the first half of the day, with cloudier conditions south. The overrunning rain due to the proximity of the frontal zone will persist across the far south (central VA and southern MD), but it should be light in nature as the best deep moisture will be suppressed in southern VA. Highs will be coolest in the south in the mid 50s, but perhaps poking into the 60s in the north.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
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Closed low aloft and associated surface system will continue sliding east across the southern US Sunday night, then turn northeast up the Atlantic Coast by Monday night. This will cause rain to overspread the region again, with temperatures remaining cool. An increasing northeast wind as the surface low strengthens will add to the rather uncomfortable weather, especially compared to recent warmth. Significant rain is possible, perhaps 1 to 3 inches. If heavy rainfall becomes concentrated, it is possible some flooding could occur, but right now, given it has generally been dry and there remains great model inconsistency about where any heavy rain may ultimately fall, do not have any plans for flood watches yet. This will no doubt be revisited by future shifts.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/... Coastal low pressure will track north along the Carolina coastline Tuesday. Forecast guidance depicts a broad area of precipitation with this system as the upper level low is nearly stacked on the coastal low. Rain is expected across the region Tuesday into Tuesday night. Bands of heavier rain are possible during this time as easterly LLJ pumps moisture into the Mid- Atlantic. Stable conditions expected with temperatures in the 50s/60s. The coastal low will be off the Delmarva coastline Wednesday and rain will come to an end across the Mid-Atlantic region. Sunshine will help temperatures get closer to 70 on Wednesday. Winds become southerly Wed night ahead of the next cold front. A cold front will pass the region Thu-Fri and showers and thunderstorms are possible. Temperatures will become above normal Thu-Fri. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...
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Lower clouds have scoured out at most locations, but linger in scattered fashion, so there is some concern with them filling in as briefly happened at DCA. There is also concern for fog developing, especially MRB, before drier air can work in. Rainfall has moved out for the night (and most of Sunday for that matter) except at CHO, where interludes of light rain will continue. Cig forecast most uncertain for CHO, as low level moisture will linger just to the south. Winds will be northerly but generally less than 15 knots. Conditions likely to return to IFR all terminals Sunday night and linger at MVFR/IFR levels through Monday night with increasing northeast winds as a coastal low makes its way northeast up the Atlantic Coast. Low ceilings and vsbys possible Tuesday-Tuesday night as rain continues.
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&& .MARINE...
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Generally marginal SCA conditions across the bay and some adjacent waters through Sunday night as high pressure nudges in from the northwest while low pressure approaches from the southwest. Added the middle Potomac portion through tonight, although latest obs suggest the area may be stabilizing. SCA likely to continue Monday and Tuesday as the low moves northeast up the Atlantic Coast. While rain will move through at times, amd not expecting thunder through Tuesday. Condtions may start to improve Wednesday.
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&& .TIDES/COASTAL FLOODING...
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A persistent onshore flow has already significantly elevated water levels in parts of the bay, with minor flooding having occurred at Straits Point this morning. Given trends this evening, have issued a Coastal Flood Advisory for St. Marys County, although it will be a threshold event. Coastal flood potential will continue through the next several days, with the greatest risk of minor flooding occurring later Sunday through Tuesday as a coastal low pressure moves northward into the region.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory until 2 AM EDT Sunday for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ536-539-542. Small Craft Advisory until 6 PM EDT Sunday for ANZ531-540. Small Craft Advisory until 6 AM EDT Monday for ANZ532>534-537- 541-543.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS/RCM SHORT TERM...RCM LONG TERM...HSK AVIATION...ADS/HSK/RCM MARINE...ADS/HSK/RCM TIDES/COASTAL FLOODING...ADS/RCM

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