Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 092029 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 329 PM EST Sat Dec 9 2017 .SYNOPSIS...
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Low pressure to our east will continue moving northeastward away from the region after the first accumulating snow of the season. A cold front will cross the region tonight. A couple clipper- like systems will graze through the area next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Light snow continues to fall across much of the area this afternoon with moderate bands of snow currently over north central and northeastern MD, as well as areas just to the east of the metro areas. Reported snowfall totals today have generally been in the 1 to 3 inch range, with the highest amounts coming out of St. Marys county in MD with 3.5 inches of snow as of lunchtime. Visible satellite imagery shows a break in the cloud cover across central WV and western, bisecting the cloud shield associated with the low pressure area to the east and a low pressure area over southern MI. Snow will begin to taper off by late this afternoon early this evening as the aforementioned low pressure area currently to our east races off to the northeast. Temperatures overnight will fall well in to the 20s for all locations, allowing any wet surfaces from todays snowfall to refreeze, posing hazardous icing conditions. Motorists and residents out and about tonight should use caution and be mindful potential icy areas. The upper level trough/clipper to our west will approach the region overnight, resulting in accumulating snows along the western slopes of the Allegheny Front. Latest hires model guidance and ensembles has snow totals reaching advisory level criteria (3-5" in a 12hr period) along the range in Pendleton and Highland counties. As a result, will be issue a WWA for this area through mid-morning Sunday when forecast soundings indicate snow should taper off.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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Dry, unseasonably chilly, and breezy conditions will persist on Sunday thanks to an Arctic airmass migrating in to the region. Icy conditions will be possible early Sunday morning thanks to the refreeze overnight. Temperatures will rebound above the freezing mark my mid morning, and with clouds clearing out by morning, sunshine will help melt those icy areas as well. Winds will likely be gusting to near 30 mph with wind chills in the teens and 20s throughout the day. Highs will struggle to get out of the 30s. A weak shortwave will pass to our north Sunday night, potentially bringing some upslope snow showers to the favored locations, but accumulations looking unlikely. Temps on Monday will moderate a bit, however remaining below normal in the lower 40s. Conditions will remain dry under partly cloudy skies. Monday night another clipper system will cross the Great Lakes region, dragging a cold front toward the Mid-Atlantic. Threat of wintry precipitation seems to be low at this time compared to earlier guidance, with the potential for some snow showers across our western slopes and light/mixed wintry precipitation possible across the far northern sections of our CWA.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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A highly amplified upper level flow pattern will continue to dominate most of the long term period with west coast ridging and east coast troughing. Low pressure will be passing north of the area early Tuesday as a shortwave trough digs southeastward toward the area. If timing remains consistent, highs in the 40s could occur early in the day, followed by cold advection behind the departing cold front. While snow will be most likely along and west of the Allegheny Front, we couldn`t totally rule out some snow showers or flurries making it farther east as well. It will also become breezy, which will persist through Wednesday in tight northwest gradient. Thermodynamic profiles become more favorable for flurries/snow showers on Wednesday as additional vorticity energy rotates through the trough. Temperatures have the potential to be quite cold Tuesday night through Thursday night -- on the order of 15 degrees below normal -- as the trough is at its deepest. Weak high pressure may nudge into the area early Thursday, but attention will then turn to the next shortwave trough diving out of central Canada sometime late Thursday into Friday. Model spread increases during this time, but some light snow is not out of the question depending on where the best forcing and moisture track. The pattern may finally buckle by Saturday, allowing high pressure to build across the area and temperatures to return closer to seasonal averages.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/...
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IFR likely with possible LIFR the remainder of this afternoon as light snow continues across the area. The best chance for restrictions will be this afternoon before snow starts to taper off from west to east by early this evening. VFR conditions will return later tonight and persist through Sunday. Light NNE winds will back out of the NW overnight and become gusty Sunday morning with gusts upwards of 25 knots. VFR conditions expected Monday, with sub-VFR possible late Monday night into early Tuesday morning. Mixed wintry precipitation will be possible at MRB and potentially BWI/MTN, but latest guidances keeps a bulk of the moisture to our north. Winds will be light out of the south Monday into Monday night. Brief visibility impacts in a passing snow shower will be possible Tuesday through Wednesday. W/NW wind gusts greater than 30 kt will also be possible during this time. Weak high pressure will likely bring calmer conditions early Thursday, but another system may bring light snow by late in the day or overnight.
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&& .MARINE...
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SCA gusts will peak over the lower tidal Potomac River and lower Maryland portion of the Chesapeake Bay the remainder of this afternoon with a lull expected this evening before northwest flow kicks in after midnight. SCA conditions expected after through Sunday, and could linger into Sunday night. Light winds are expected Monday before winds increase again ahead of a clipper late Monday night. A cold front will push through early Tuesday, bringing increasing west/northwest winds which will persist through Wednesday. High end Small Craft Advisory conditions appear likely, and there could be a period of gales. Weak high pressure should bring diminishing winds late Wednesday night into Thursday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Winter Weather Advisory until 9 PM EST this evening for DCZ001. MD...Winter Weather Advisory until 9 PM EST this evening for MDZ004>006-011-013-014-016-018-503>508. Winter Storm Warning until 9 PM EST this evening for MDZ017. VA...Winter Weather Advisory until 7 PM EST this evening for VAZ025- 026-029-030-036>040-050-051-501-502-505-507-508. Winter Weather Advisory until 9 PM EST this evening for VAZ052>057-506. WV...None. MARINE...Small Craft Advisory from midnight tonight to 6 PM EST Sunday for ANZ530>533-535-536-538>542. Small Craft Advisory until 4 PM EST this afternoon for ANZ533- 541-542. Small Craft Advisory until 6 PM EST Sunday for ANZ534-537-543.
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&& $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...ADS AVIATION...BKF/ADS MARINE...BKF/ADS

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