Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 082000 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 300 PM EST Fri Dec 8 2017 .SYNOPSIS...Low pressure system will impact the area tonight through Saturday. High pressure will return Sunday into Monday. Another low pressure will impact the area on Tuesday. Weak high pressure builds over the area for the second half of next week. && .NEAR TERM /THROUGH SATURDAY NIGHT/...Low pressure will get organized and gather strength off of the southeast coast late tonight and track northeast parallel to the mid-Atlc coast Sat. To the nw of the sfc low track expect a swath of moderate to occasional heavy snow late tonight into Sat. 12Z global model guidance remained consistent with the previous 00Z and 12Z cycles from the past 12 to 24 hrs. This boosts confidence for supporting higher snow totals near and south of the I-95 corridor where deterministic and ensemble QPF show half inch or greater QPF. Amplifying upper level trough and strengthening upper level divergence will provide large scale forcing for upward vertical motion for significant early season snows especially across our southeast counties. Refer to our local winter page for specific snow totals and probabilities. Precip will end by 21Z Sat as low moves farther offshore and NW winds kick in. && .SHORT TERM /SATURDAY NIGHT SUNDAY NIGHT/... Low pres moves farther offshore with precip ending but upper level trof crossing the area will result in snow showers over the mtns with a couple of inches of accumulation likely. Turning colder and windy late Sat night and Sun. && .LONG TERM /MONDAY THROUGH FRIDAY/... A highly amplified upper level flow pattern will continue to dominate the long term period with west coast ridging and east coast troughing. We`ll be in between shortwave troughs on Monday, so dry but chilly weather is expected. A surface low will be moving through the Great Lakes Monday night. Model consensus has the warm advection arm of this system dry except along the Appalachian crest, but if this changes, there could be mixed precipitation potential. The associated cold front and upper trough axis will swing through the area Tuesday and Tuesday night. Winds could be quite gusty behind the front. Upslope snows look likely, while there could be some snow showers or even squalls east of the mountains. Surface temperatures will likely remain above freezing (40s for early highs) until very late in the day though. The core of the cold air will be over the area Wednesday into Wednesday night. It`s possible some areas could fail to reach freezing for highs on Wednesday, then fall into the teens Wednesday night. There could be additional opportunities for flurries during this time. High pressure will nudge into the area from the south on Thursday, but the next shortwave trough will approach on Friday, likely driving another surface low through the Great Lakes. There`s some additional spread in the guidance by this point, although there will be a chance of wintry precipitation across parts of the area. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... Developing IFR/LIFR conditions in light/moderate snow late tonight into Sat. Precip ends by 21Z Sat with improving conditions Sat evening. Winds strengthen from the NW Sat night with gusts up to 30 kt possible into Sun. Winds diminish Sun night. An interval of sub-VFR clouds is possible Monday night. Brief visibility impacts in scattered snow showers will be possible Tuesday into Tuesday night. Wind gusts over 30 kt possible Tuesday through Wednesday. && .MARINE... Light and variable winds through this evening then increasing late tonight across the southern waters. SCA issued earlier. Winds strengthen across all waters Sun with solid SCA conditions everywhere. Chance of gales appears relatively low attm. Light southerly flow is expected Monday with weak high pressure. Small Craft Advisory conditions could begin Monday night, but become more likely with winds out of the west-northwest Tuesday into Wednesday after a cold front sweeps across the area. A period of gale force winds will also be possible. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Winter Weather Advisory from midnight tonight to 4 PM EST Saturday for DCZ001. MD...Winter Weather Advisory from midnight tonight to 4 PM EST Saturday for MDZ006-011-013-014-503>508. Winter Weather Advisory from 4 AM to 4 PM EST Saturday for MDZ004-005. Winter Storm Warning from 7 PM this evening to 4 PM EST Saturday for MDZ016>018. VA...Winter Weather Advisory from 7 PM this evening to 4 PM EST Saturday for VAZ025-026-029-030-040-501-507-508. Winter Weather Advisory from midnight tonight to 4 PM EST Saturday for VAZ036>039-050>056-502-506. Winter Weather Advisory from 4 AM to 4 PM EST Saturday for VAZ505. Winter Storm Warning from 7 PM this evening to 4 PM EST Saturday for VAZ057. WV...None. MARINE...Small Craft Advisory from midnight Saturday night to 6 AM EST Sunday for ANZ530>533-538>542. Small Craft Advisory from midnight tonight to 4 PM EST Saturday for ANZ533-541-542. Small Craft Advisory from midnight tonight to 6 AM EST Sunday for ANZ534-537-543. && $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...LFR LONG TERM...ADS AVIATION...ADS/LFR MARINE...ADS/LFR is the U.S. government's official web portal to all federal, state and local government web resources and services.