Area Forecast Discussion
Issued by NWS Sterling, VA

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683 FXUS61 KLWX 151916 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 216 PM EST Mon Jan 15 2018 .SYNOPSIS... High pressure will weaken and slide toward the east coast through tonight. A cold front will approach the area Tuesday before passing through Tuesday night into Wednesday. Low pressure will develop along this boundary offshore later Wednesday before high pressure settles to our south Thursday. High pressure will remain to our south through the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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Initial shortwave has departed east leaving behind stronger than anticipated subsidence and a brief window of clear. Clouds will rebuild this evening as high pressure continues to weaken and move away and deeper troughing approaches from the west. Another cold night is expected despite the clouds with lows generally in the 20s. Light snow likely moves in/develops over the western ridges and into northwestern Maryland by daybreak.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... The much awaited cold front associated with the approaching trough will move slowly eastward into the area during the day Tuesday. As heights fall and lift increases, anticipate snow (mainly light) to continue developing eastward, eventually reaching the NW suburbs of DC/Baltimore after dark. There is still some uncertainty in timing, but the most likely scenario is one where snow moves into the Shenandoah Valley and parts of north-central Maryland (northern Baltimore to Frederick County MD) between 4 and 7 PM, pushing across I-95 between 8 and 11 PM. The steadiest snow from the Shenandoah Valley eastward to the metro areas should be between late Tuesday evening and early Wednesday morning, likely impacting the Wednesday morning commute. Steadier snow should enhance/linger across portions of central Virginia (the Charlottesville area) to southern Maryland through Wednesday morning as a wave of low pressure develops offshore. Meanwhile, dry air advecting in from the northwest should cause snow to cease across much of eastern West Virginia, northern Virginia and northern Maryland by mid-morning Wednesday. In general, anticipating 1-2 inches across much of the area, with 2-4 inches across the higher elevations and central Shenandoah Valley into parts of central Virginia where higher ratios/stronger forcing and moisture will be juxtaposed. Have issued an advisory across the Allegheny Front and northern Maryland/eastern West Virginia where confidence is highest, and hoisted a Special Weather Statement for a potentially hazardous Wednesday morning commute for the I-95 corridor. Clearing and breezy conditions are expected Wednesday night as the cold front pushes east, ushering in another Arctic airmass. Cold wind chills are possible again over the higher elevations which could warrant an advisory Wednesday night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... High pressure will remain to our south over the southeastern CONUS into the Atlantic Thursday through the weekend. A west to southwest flow will allow for a moderating trend in temperatures. In fact...this weekend max temps in the 50s are most likely. Dry conditions will likely persist during this time as well. Overall there is good pattern agreement amongst guidance for the long term period. On Thursday morning, the upper level trough will be exiting the east coast, giving way to a shortwave ridge and surface high pressure building across the Mid South. While high temperatures will return closer to seasonal normals, Thursday night will likely be cold (teens/20s) again with light winds and mostly clear skies. Low pressure will track into the Great Lakes later Sunday into Monday. The cold front associated with the low will approach our area during this time. A southwest flow will continue to usher in milder conditions...but increased moisture from the Gulf of Mexico and the forcing from the front will cause increasing chances for precipitation. Timing is uncertain this far out. && .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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MVFR cigs have lifted as stronger than anticipated subsidence behind departing shortwave aloft moves overhead. Scattered MVFR possible overnight in onshore flow. -SN with possible restrictions likely reaches MRB around daybreak. Patchy fog is hinted at east of the Blue Ridge tonight by some guidance, but left out for now given seemingly low likelihood with cloud cover, though non- zero potential given onshore flow. Sub-VFR (IFR possible at times) likely Tuesday night in -SN. VFR should return by midday Wednesday. Winds should be light today through Tuesday, then become NW and blustery by Wednesday. High pressure will settle to the south and east for Thursday through Saturday. A west to southwest flow is expected during this time. VFR conditions are most likely during this time.
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&& .MARINE... Generally light winds expected through Tuesday. NW winds increase likely to SCA levels early Wednesday morning. High pressure will settle off to the south and east Thursday through the weekend. A west to southwest flow is most likely during this time. A Small Craft Advisory may be needed for portions of the waters Thursday. Winds may approach SCA criteria Friday into the weekend as well, but confidence is low. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Winter Weather Advisory from 5 AM to 8 PM EST Tuesday for MDZ003-501-502. Winter Weather Advisory from 4 PM Tuesday to 7 AM EST Wednesday for MDZ004>006-507. VA...Winter Weather Advisory from 5 AM to 8 PM EST Tuesday for VAZ503. WV...Winter Weather Advisory from 5 AM to 8 PM EST Tuesday for WVZ050>053-055-501>505. MARINE...None. && $$ SYNOPSIS...BJL NEAR TERM...DHOF SHORT TERM...DHOF LONG TERM...BJL AVIATION...DHOF MARINE...DHOF

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