Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200210 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 910 PM EST Sun Nov 19 2017 .SYNOPSIS... High pressure will build to our south tonight through Monday night. The high will move offshore Tuesday and a cold front will pass through Tuesday night into Wednesday. High pressure will build back overhead later Wednesday through Thanksgiving Day. Coastal low pressure will likely move well out to sea Friday and a cold front will pass through Saturday. && .NEAR TERM /THROUGH MONDAY/...
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Surface low pressure is racing toward the Canadian Maritimes this evening while high pressure is centered near Memphis. Water vapor loops show the mid/upper level shortwave over top of the area, which is allowing stratocumulus clouds to persist. Wind gusts have diminished compared to the daylight hours, but random gustiness will remain possible through the night due to the cold air advection and pressure rises. PBZ radar shows snow showers continuing to advect into the Appalachian Mountains. So far, snow observations we`ve received have not amounted to much, but due to the targeted nature and intensity of the convective elements, will allow the Winter Weather Advisory to continue. Traffic cameras indicate roads are becoming snow covered in Garrett County, so that`s likely the case further south as well. A few flurries and sprinkles are making it east of the mountains but will have little impact with temperatures in the upper 30s to around 40. Overnight, snow showers along the Allegheny Front should quickly wind down behind the shortwave and stratocumulus should clear. Temps will bottom out below freezing in most of the area, except the warmest urban centers and along the warmer large bodies of water (Potomac/Chesapeake). On Monday, high pressure should continue building eastward, reaching eastern North Carolina by day`s end. This will cause winds to shift from northwest to southwest, but warm advection will be slow, so we still expect Monday to be chilly, with highs struggling to reach 50. The lighter winds and greater sunshine under a shortwave ridge will likely make Monday feel a little more comfortable, especially in the afternoon.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... High pressure will shift east off the coast Monday night and Tuesday, allowing southwesterly flow to dominate. While Monday night looks radiational thanks to diminishing winds and clear skies near the center of the high, by Tuesday sunshine and warmer air aloft will translate to warmer surface temps, with most places rebounding 5-10 degrees above Monday`s expected highs. Tuesday night, a cold front will approach from the northwest while a shortwave will spawn a coastal low near the Outer Banks. Still some question regarding how far west the rain shield from this low makes it, but most guidance now shows rain reaching southern Maryland, and a fair number have rain reaching Baltimore and Washington proper. Thus, have chance pops for the big cities and likely in southern MD. Further west, odds are considerably lower. It should overall be a milder night thanks to the warm advection ahead of the cold front combined with increased cloud cover, with lows mostly above freezing. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... High pressure will build into the region Wednesday through Friday night. Dry conditions expected with plenty of sunshine each day and mainly clear skies at night. Despite the daytime sunshine, temperatures each period will be about 5 to 7 degrees below average with highs in the upper 40s to near 50 and lows in the upper 20s to near 30. A storm system over eastern Canada will bring a cold front toward and across the mid-Atlantic Saturday and Saturday night. There is a chance for a few rain showers along the Mason-Dixon region Saturday with a chance of rain and snow showers in the Appalachians and along the Mason-Dixon regions Saturday night. Temperatures will be closer to average. A gusty northwest wind will usher in cold air into the region Sunday. With that, a chance of snow showers are expected in the Appalachian Mountains. Below average temperatures expected to retake the region. && .AVIATION /02Z MONDAY THROUGH FRIDAY/...
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VFR overall through the TAF period. There could be a stray sprinkle or flurry this evening but with little impact. Winds have generally diminished, but a few random gusts to 20 kt remain possible through the night. Winds may return to the 20 knot range during the day Monday. Tuesday night is the only real chance of sub- VFR as a low pressure system could bring a bit of rain, which may reduce cigs and vis for a time. Still uncertain just how far west this precip gets. VFR conditions Wednesday through Thursday night. Winds northwest 5 to 10 knots Wednesday. Winds northwest around 5 knots Wednesday night. Winds becoming light and variable Thursday and Thursday night.
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&& .MARINE...
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Winds have diminished substantially, with most observations being 20 knots or less. Will continue the Small Craft Advisory for all waters through the night, as gustiness may increase at times due to cold air advection and pressure rises. Am not thinking these factors will be strong enough to pull down any gale force gusts, though a few gusts around 30 knots remain possible on the more open waters. SCA continues most waters through Monday as high pressure shifts east to our south. However, winds may diminish across the southern half of the waters by midday. Winds probably go sub SCA on Monday night but may go back to SCA Tuesday ahead of the next cold front, which passes late Tuesday night. SCA possible behind cold front Wednesday, may be diminishing Wednesday night. Winds light and variable Thursday and Thursday night.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...Winter Weather Advisory until 11 PM EST this evening for WVZ501-505. MARINE...Small Craft Advisory until 6 PM EST Monday for ANZ530>534- 537>543. Small Craft Advisory until 10 AM EST Monday for ANZ535-536.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS/RCM SHORT TERM...RCM LONG TERM...KLW AVIATION...ADS/RCM/KLW MARINE...ADS/RCM/KLW

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