Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 171547 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1047 AM EST Sat Feb 17 2018 .SYNOPSIS...
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Low pressure will track northeastward along a stalled frontal boundary well to our south today and tonight. High pressure will build in from the west on Sunday, migrating offshore by Monday. Low pressure will move northeastward toward the Great Lakes Monday, lifting a warm front northward through our region. A cold front is poised to approach the region during the latter half of the work week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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High and mid-level clouds streaming over our area from the southwest this morning, but ample sunshine has greeted much of the region this afternoon. Temperatures in the middle to upper 30s for most this morning, but with the clouds encroaching in response to an approaching mid-level trough and surface low pressure over the Tennessee River Valley, we won`t see them warm too much more, topping out near 40 in the warmest locales. Skies turn mostly cloudy for all by this afternoon and moisture begins to increase from southwest to northeast over the region. Despite temperatures 5 to 10 degrees above freezing today, do think as precipitation spreads across the region, wet bulbing will occur with dewpoint depressions on the order of 10-15F this morning. Precipitation will overspread the area early this afternoon to our southwest, reaching the metro areas mid to late afternoon. The precip may start as rain before sufficient cooling occurs, especially along and south of I-66, then a transition to snow/sleet. Expect snow at the onset across our northern zones with colder temperatures at the surface and aloft there. Precipitation picks up in earnest by this evening as favorable lift moves closer to our region with a potent shortwave nearby and a the right entrance region of the jet moving overhead. Low pressure will quickly develop off the VA/MD coast where a strong baroclinic zone resides, then race off to the northeast. Precipitation will end for most by midnight. Temperatures will fall to near freezing in the metro areas, and below freezing to the north and west overnight. This will allow for potential icy spots early Sunday morning, so use caution if out traveling. Thinking remains that the northern third of our CWA remains mostly snow through the event, with Southern MD seeing snow/sleet mix changing to plain rain the quickest. Metro areas in between will reside near the snow/sleet/rain transition line, and where that resides will obviously impact accumulations and ptype. Will keep advisories as are for now, with no significant changes made to the forecast package from earlier this morning. We will digest the remaining 12z guidance to determine where adjustments, if any, need to be made. As always, visit our winter weather page for the latest on accumulations and timing at weather.gov/lwx/winter.
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&& .SHORT TERM /THROUGH SUNDAY NIGHT/...
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High pressure quickly moves in behind the exiting low pressure area to the northeast, resulting in a dry and clear conditions. After a cold and perhaps icy start to the morning, temperatures will rebound nicely, topping out in the mid 40s to lower 50s region wide. High pressure shifts offshore Sunday night, keeping a light return flow over the region and temperatures above normal.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/... Warm front slides to our north on Monday in return flow as high moves well to our east. PoPs for rain likely in our west... lesser to the east. Temps in the 50s. Another surge of much above normal warmth is expected for the middle of next week, followed by increasing rain chances by the end of the week. An anomalously strong upper level ridge will be centered off of the southeast United States coastline Tuesday morning with deep southwest flow entrenched across the region. This will lead to dry and very warm conditions on Tuesday with temperatures likely on the order of 25 degrees above climatological normals for mid-late February. High temperatures are currently forecast to reach the 70s area-wide, with lows Tuesday night holding in the 50s. A cold front will then be on the approach by Wednesday, crossing in the late Wednesday - Thursday time period, although timing differences exist between model solutions, with 17/00z ECMWF slower, and 17/00z GFS quicker with frontal passage. Will favor the slower ECMWF solution as the less progressive ECMWF usually fares better in these types of situations. This would keep Wednesday quite warm and relatively dry, with increasing chances for rain Wednesday night and Thursday. Temperatures will trend downward after frontal passage. The boundary will then remain nearby for later Thursday and Friday with strong southwest flow continuing aloft as upper ridge remains intact over the southeastern US. This will lead to additional rain chances into Friday, and temperatures considerably cooler than mid- week but still likely near or above normal. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
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IFR and possibly LIFR CIGS/VIS at times late this afternoon into tonight as wintry precipitation moves in to the area from the southwest. Snow could be briefly heavy in bands. The system quickly exits the terminals by 04z, resulting in a return to VFR conditions, which is expected to prevail through Sunday night. Next weather system is a warm front that will most likely bring some period of MVFR on Monday. Predominantly VFR expected Tuesday through Wednesday with gusty southwest flow. Chances for showers will be increasing late Wednesday and Wednesday night.
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&& .MARINE...
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Gusty winds over the main stem of the Potomac and Bay subsided earlier this morning, thus the SCA that was in effect was allowed to expire. Winds will remain below advisory criteria through Monday as high pressure traverses our region and moves offshore. Small Craft Advisories may be needed Tuesday through Wednesday with gusty southwest winds. With warm air temperatures expected over considerably cooler waters, the strongest gusts will likely be observed along the shorelines.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Winter Weather Advisory until midnight EST tonight for MDZ501. Winter Weather Advisory from 2 PM this afternoon to midnight EST tonight for MDZ003>006-502-503-505-507-508. VA...Winter Weather Advisory until midnight EST tonight for VAZ025>027-029-030-040-501-503-504-507-508. Winter Weather Advisory from 2 PM this afternoon to midnight EST tonight for VAZ028-031-505. WV...Winter Weather Advisory until midnight EST tonight for WVZ055- 502-505-506. Winter Weather Advisory from 2 PM this afternoon to midnight EST tonight for WVZ050>053-504. Winter Storm Warning from 2 PM this afternoon to 2 AM EST Sunday for WVZ501-503. MARINE...None.
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&& $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF/CS LONG TERM...MM AVIATION...MM/CS/BKF MARINE...MM/CS/BKF

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