Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 060349 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1049 PM EST Tue Dec 5 2017 .SYNOPSIS... A cold front will move through the area tonight. Weak high pressure returns to the area for Wednesday and Thursday. Low pressure will pass to the east Friday and Friday night, then another low pressure may cross the region Saturday and Saturday night. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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A cold front is moving through the Potomac Highlands late this evening. A southerly flow ahead of the boundary has allowed for mild conditions...but plenty of clouds and showers are ahead of the boundary over our area. The cold front will pass through from northwest to southeast...first through the Potomac Highlands and Shenandoah Valley by midnight...then through the Baltimore and Washington Metro areas between 1 am and 3 am...then across southern Maryland Rain by 5 am. A wind shift to the northwest is expected behind the boundary and noticeably chillier conditions are expected. Northwest winds will gust around 30 to 45 mph for an hour or two behind the boundary. Showers may hang around for a couple hours even after the frontal passage due to a southwest flow aloft and shortwave energy passing through. However...drier air will eventually win over causing precipitation to end by daybreak for most locations. The one exception may be across southern Maryland where light rain may still be hanging around. Little if any snow is expected...and the best chance will be across the ridge tops of the Allegheny Highlands. Drier air should take over before temps are cold enough for any snow for most locations. Lows by morning will be in the 30s/40s.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... Surface ridging will build in behind the front for Wednesday, although still expecting a lot of high clouds with strong southwest flow aloft. Otherwise, temperatures will be more seasonable with highs in the 40s to around 50F. The frontal zone will settle southeast of the area along the VA/NC coastline, and will set the stage for a couple waves of low pressure and moisture to ride along the boundary through the end of the week and weekend. The first will occur Wednesday night and remain largely south/east of the area, although high clouds will remain, and perhaps a shower can make it into our southern waters or far southeastern Maryland. Otherwise, dry weather Wednesday night with lows in the 30s. Quiet weather expected to continue through Thursday with high pressure over the region. Temperatures on the cool side, but within 5 degrees or so of normal with highs in the 40s. A second more prominent wave will push northeastward along the baroclinic zone to our south/east Thursday night out ahead of an approaching digging full latitude trough. Questions remain on how far north/west moisture from this wave can make it, and is discussed further in the long term section below. Either way, Thursday night likely remains dry with lows in the 20s/30s. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Upper level trough will continue to deepen on Friday while the frontal zone remains to our southeast. Upper level energy ahead of this trough will result in the development of a surface low off the North Carolina coast on Friday into Saturday... and it will move northeast away from our region. Likely areas to see some type of precipitation is the southeast of our CWA. A second system to watch for Saturday is an upper level low that will move through our area on Saturday into Sunday. There is some disagreement on the guidance on how much precipitation we might get from this system but instability associated to it suggests there is the possibility of snow squalls. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
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A cold front will pass through the terminals overnight...first across KMRB around 03z..then across KIAD and KCHO between 5 and 7z...and across KDCA...KBWI and KMTN between 7z and 9z. A few showers and period of MVFR conditions are possible ahead of the front. A wind shift to the northwest is expected behind the front and brief gusts around 30 knots are possible especially across the northern terminals. VFR conditions will return behind the front by Wednesday morning and continuing through Thursday night. Southerly winds which may gust up to about 20 knots at times today will shift northwest and gust up to 20 knots again after frontal passage later tonight and into Wednesday morning. VFR conditions expected early Friday. Sub-VFR conditions possible Friday night into Sunday as some rain/snow showers could move through the terminals.
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&& .MARINE...
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A cold front will pass through the waters overnight. A wind shift to the northwest is expected behind the boundary with gusts around 30 knots likely. A few gusts up to 35 knots cannot be ruled out...and this will be monitored overnight. A secondary surge of winds may occur Wednesday night into Thursday and a SCA may be needed again. Winds are expected to stay below small craft advisory threshold Friday into Saturday night. Winds may increase enough on Sunday to need a small craft advisory.
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&& .TIDES/COASTAL FLOODING...
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Anomalies should drop behind a cold front overnight as an offshore flow develops.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until midnight EST tonight for DCZ001. MD...None. VA...Coastal Flood Advisory until midnight EST tonight for VAZ054. WV...None. MARINE...Small Craft Advisory until 6 PM EST Wednesday for ANZ530>543.
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&& $$ SYNOPSIS...MM NEAR TERM...BJL/MM SHORT TERM...BJL/MM LONG TERM...IMR AVIATION...BJL/MM/IMR MARINE...BJL/MM/IMR TIDES/COASTAL FLOODING...BJL

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