Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 161056 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 556 AM EST Thu Nov 16 2017 .SYNOPSIS... High pressure will build into the region today through Friday. A strong cold front will approach the area Saturday, then cross Saturday night. High pressure will build to the south of the region late Sunday into the first half of next week. && .NEAR TERM /THROUGH TONIGHT/...
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550 AM update...Have issued a Wind Advisory for elevations above 1500-2000 feet (Blue Ridge zones and ridges of Allegheny Front) for today. RAP/HRRR are insistent on 40-45 knot winds below 1000 feet AGL in these areas, and upstream obs of widespread gusts of 30-35 kts over Ohio during diurnal min suggests 40 knot gusts are probable enough to warrant a headline. The wind field remains this evening but uncertainty in mixing height decreases, so for now terminate the advisory at 6 PM. Brief clearing is taking place this morning, but scattered to broken cumulus and a few sprinkles (especially north of the Potomac River) are expected by mid to late morning through this afternoon. Strong and gusty northwest winds are expected in the lowlands by later this morning through the afternoon as well with gusts of 30 to 40 mph possible. Previous discussion...Hedged the high temperature forecast toward the upper tercile of guidance since temperatures often overperform in a downsloping regime. The colder airmass moving in should begin to overwhelm downsloping effects east of the mountains after midday, with high temperatures likely being observed by early afternoon and then falling thereafter. Upslope showers will likely continue through the day and into the first part of tonight, mixing with and changing to snow by mid-morning this morning with colder air rushing in. Precipitation should be light as the moisture layer is relatively shallow, so accumulations should remain under an inch. The moisture may become shallow enough to support a period of freezing drizzle this evening along the western slopes of the Allegheny Front, but deeper mixing/gusty winds may preclude this so it`s of low confidence at the moment. A secondary pressure surge occurs tonight which should keep winds elevated into Friday morning, especially over the ridges.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Friday should be mainly sunny and much cooler as cool high pressure moves overhead. The benign weather will be short-lived, however, as a strong upper trough digs into the Great Lakes. Strong surface cyclogenesis is forecast to the northwest of the CWA Friday night into Saturday. This will drag a strong cold front into the region by Saturday evening. The slow trend has continued in the guidance and as such have backed off on PoPs during the day Saturday (though non-zero in strong warm advection), then ramp up quickly Saturday evening. A strong southwesterly low-level jet of 60+ knots at 3000-5000 feet) would suggest a potential for 40-45 knot surface gusts over the ridges, and in the valleys in any heavier showers ahead of the front, though mixing becomes more difficult at lower elevations in SW flow especially given the unfavorable time of day (evening and overnight hours). Precipitation should change to snow showers over the western ridges of the Allegheny Front after midnight after the cold front passes and winds turn northwest. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... The area will be on the back side of a strong cold front Sunday morning with gusty northwest winds and below normal temperatures. With strong northwest flow, upslope snow showers will be in progress across the higher elevations near and along the Allegheny Front, and some accumulation is likely. High temperatures will range from the 30s near the Allegheny Front to around 50F in central VA and southern MD. Much quieter weather is then anticipated for Monday and Tuesday as high pressure builds overhead. Temperatures will start below normal Sunday night into Monday but moderate back towards climatological normals by Tuesday. The next chance of precipitation will come in the middle of next week as a fast moving northern stream trough moves towards the area. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... Mainly VFR through Friday night. Scattered-broken cumulus expected between 4000 and 6000 feet today. Gusty NW winds of 20 kts with gusts to 30 knots are expected as well today, peaking in the afternoon and only slowly diminishing this evening. Winds should fall below 10 knots by about midday Friday. Some flight restrictions are possible by later Saturday, becoming more likely Saturday night as a strong cold front approaches. SW winds will also begin to increase Saturday, with low-level wind shear likely by Saturday afternoon and persisting into Saturday night. Winds at 2000 feet may approach 50 knots during this time. Primarily VFR conditions are expected Sunday through Tuesday. Gusty northwest winds will be the main aviation weather concern on Sunday. Winds lessen Sunday night and Monday as high pressure builds towards the region. && .MARINE... A Small Craft Advisory is in effect for most waters starting at 6 AM, then all waters after 10 AM through noon Friday as strong and NW winds are anticipated behind a cold front. Gale force gusts are possible late this afternoon and evening as well, but these winds are above 2000 feet so confidence is too low for a headline at the moment. Gusts diminish Friday, then resume late Friday night into Saturday as southwest winds increase ahead of an approaching strong cold front. Gales are possible Saturday into Saturday night as well. SCA gusts likely and gale conditions possible behind strong cold front on Sunday and into Sunday night. SCA conditions may continue through Monday. && .TIDES/COASTAL FLOODING...
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DC SW Waterfront will come close but should fall just short of minor tidal flooding this morning. Strait`s Point may come close again the next tide cycle (around midday) but by that time anticipate northwest flow to cause anomalies to decrease. If winds are delayed even briefly or off slightly in trajectory from the going forecast, though, and advisory would be needed.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Wind Advisory until 6 PM EST this evening for MDZ501. VA...Wind Advisory until 6 PM EST this evening for VAZ503-504-507- 508. WV...Wind Advisory until 6 PM EST this evening for WVZ501-503-505- 506. MARINE...Small Craft Advisory until noon EST Friday for ANZ530>532-539- 540. Small Craft Advisory until 6 PM EST Friday for ANZ533-534-537- 541-543. Small Craft Advisory from 9 AM this morning to 6 PM EST Friday for ANZ542. Small Craft Advisory from 9 AM this morning to noon EST Friday for ANZ535-536-538.
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&& $$ SYNOPSIS...DHOF NEAR TERM...DHOF SHORT TERM...DHOF LONG TERM...MM AVIATION...MM/DHOF MARINE...MM/DHOF TIDES/COASTAL FLOODING...DHOF

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