Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210519 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1219 AM EST Sat Jan 21 2017 .SYNOPSIS...
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A front will remain stalled south of the area through Today. Low pressure will impact the area Sunday through Monday before moving away Tuesday. A cold front will pass through the area Wednesday into Wednesday night and an upper-level trough may build overhead late next week.
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&& .NEAR TERM /THROUGH TODAY/...
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Dense Fog Advisory has been issued through 9 AM for locations where visibilities are already a quarter mile or less (or are expected to be shortly). Expansion to the advisory may be needed later this morning further east across the DC/Balt metros as the stratus deck continues to lower. Previous Discussion... Warm front is analyzed across central NC this evening, then curving northward along the Appalachians in typical cold air damming fashion. Meanwhile heights are building aloft. Thus no organized precip overnight, although westerly flow aloft will be overrunning the moist southeast flow at the surface, so some patchy drizzle could occur at times through Saturday morning. Thick stratus remains banked along the east side of the Blue Ridge and then spills across into western Maryland...and expect this to remain constant into Saturday morning, if not through the entire day. Fog will be in two regimes tonight...due to lowering stratus in the north/east, and with a radiational component in the Shenandoah Valley. How limited the visibilities become remains in question at this time. Have lowered temperatures tonight west of the Blue Ridge due to the radiational cooling, and raised them in the east due to elevated dew points. Lows will be in the 40s except some upper 30s in the west and near the PA border. Clouds are most likely to break again on Saturday in the Virginia Shenandoah Valley and adjacent West Virginia, where there is a good shot of temperatures spiking into the 60s. Have kept highs below guidance (lower to mid 50s) in the north and east, but any breaks in the clouds could easily push temperatures 5 degrees higher.
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&& .SHORT TERM /TONIGHT THROUGH MONDAY/... Guidance continues to show a significant coastal storm system Sunday and Monday, though they continue to shift on the details. Today`s guidance has shifted west a bit, and somewhat weaker. Overall however, still expect rain to overspread the area Sunday with the first wave of low pressure, then another surge of rain late Sunday night or early Monday with the main center. This second, stronger low looks weaker than yesterday but still will bring some breezy conditions. A wind advisory is still not out of the question on Monday, but the odds look lower than yesterday given the weaker low and its shift westward. Generally, between the two waves of low pressure, looks like most of the region should end up with around an inch of rain, with potential for up to two inches. Given recent dry weather, this probably isn`t a big flood threat, especially given the long period over which the rain is expected to fall. Also given the shift westward on the guidance, the small threat of snow that some models showed yesterday is looking less likely today. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Surface low pressure over or near our area will continue to push northeast away from our region Monday night into early Tuesday. Precipitation associated to it should be tapering off, mainly east of the Blue Ridge during this time... while higher elevations could experience different p-types Monday night. Dry conditions expected on Tuesday into Wednesday -some showers possible at higher elevations per some GEFS members- before another cold front moves through the region Wednesday night into early Thursday, with limited precipitation. Upper trough to our west will slowly move east, bringing precipitation west of the Allegheny Front Thursday into Friday. Some precipitation could reach east of the Blue Ridge Thursday night into Friday, but still highly uncertain if it will, and what p-type. High temperatures will be in the 40s and 50s Tuesday and Wednesday, decreasing into the 30s and 40s on Thursday and Friday. Low temperatures will be in the 30s and 40s, with Thursday night being the coldest. && .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/... Aviation forecast has become more clear now that we are heading into the overnight hours and the stratus deck is lowering. BWI remains the only terminal at MVFR at this writing, but should fall into IFR at any time. Then the only question is whether LIFR or lower conditions are achieved (think there`s a good chance, especially inland terminals). Vsbys may be a little more variable, and there could be patchy drizzle at times. Statistical guidance indicates IFR cigs will persist all day Saturday, but forecast soundings indicate a little mixing, and have thus shown a trend to MVFR by afternoon. If a complete break out from the overcast would occur, MRB/CHO would be the most likely candidates. Winds should remain light and southeast through Saturday night. Rain moving in late Saturday night will cause restrictions to return for Sunday and Monday. Winds will also likely start getting gusty by Sunday night and Monday, generally from a northeast direction. Low pressure system will move away Monday night into early Tuesday and precipitation will be tapering off during this time. Breezy conditions expected, with wind gusts reaching 20 kts... decreasing into Tuesday night. Dry conditions expected Tuesday into Wednesday. Some showers possible Wednesday night. So, sub-VFR conditions possible Monday night into Tuesday, becoming VFR sometime Tuesday and remain into Wednesday. && .MARINE... Sub-SCA conditions through Saturday night with southerly winds tonight, gradually turning southeasterly on Saturday. Winds increase markedly for Sunday and Sunday night out of the east/northeast with Small Craft Advisory conditions likely Sunday, with Gales possible Sunday night. Low pressure system will move away Monday night into early Tuesday and precipitation will be tapering off during this time. Breezy conditions expected, with wind gusts reaching 20 kts... decreasing into Tuesday night. Dry conditions expected Tuesday into Wednesday. Some showers possible Wednesday night. Small craft advisory expected for Monday night into Tuesday night as winds diminish below the threshold. && .TIDES/COASTAL FLOODING... Onshore flow will strengthen later Sunday through Monday as a coastal storm moves northward into the area. Tidal flooding is possible during this time. The flow will turn offshore later Monday night and Tuesday as the storm moves away. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Dense Fog Advisory until 9 AM EST this morning for MDZ003>006- 502-507. VA...Dense Fog Advisory until 9 AM EST this morning for VAZ025>031- 504. WV...Dense Fog Advisory until 9 AM EST this morning for WVZ050>053- 055-502-504-506. MARINE...None.
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&& $$ SYNOPSIS...RCM NEAR TERM...MSE/ADS/RCM SHORT TERM...RCM LONG TERM...IMR AVIATION...ADS/IMR/RCM MARINE...IMR/RCM TIDES/COASTAL FLOODING...

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