Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200151 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 851 PM EST Sat Jan 19 2019 .SYNOPSIS... A strong storm system will move northeastward across the region tonight. Arctic high pressure will gradually build across the region Sunday through Tuesday. A slow moving cold front will slide into the region Wednesday, with another strong storm system possibly moving across the region late in the week. && .NEAR TERM /THROUGH SUNDAY/... Precip has transitioned to sleet and rain across north central and northeast MD based on spotter reports and dual pol CC product. Snow remains the main p-type across Allegany County MD where up to 4.5 inches of snow have been reported. It should become predominantly fzra across western Allegany later tonight and rain everywhere else as temps continue to rise. All of the warnings and advisories should be able to be canceled by 06Z Sun except in western Allegany where temps may still be around freezing. Looking at tomorrow, NW winds will kick in early in the day and may continue all night and all day Monday. Wind advisories may need to be extended into Monday and Wind Chill Advisories will also be needed. Previous afd... The system pulls quickly to the northeast early Sunday, with precip pulling out near or just after dawn, mostly in the form of rain. Strong pressure gradient developing on the back side of the low will likely lead to widespread gusts of 40-45, perhaps 50 mph, so have issued wind advisory for most of the CWA on Sunday. Otherwise, the theme of the day will be winter`s return as cold air rushes back into the region. Temps which will start out in the fairly mild 40s in the metro will end up in the 20s by the end of the day, with whatever liquid remains likely freezing up. Perhaps not quite a "flash" freeze technically, but definitely a hazard. Further west will not start out so lucky, with temps likely stuck in the 30s most of the night, but they too will end up well below freezing by day`s end. Wind chills will also plummet, with readings likely into the single digits by nightfall. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... Low pressure will continue slowly moving away Sunday night through Monday night as arctic high pressure slowly builds in. This will keep the winds from diminishing rapidly, with only a slow decline. Combined with bitterly cold arctic air, wind chill advisories will almost certainly be needed across most of the CWA, and its possible some of the high mountains out west might need a wind chill warning. The northwest winds will likely also result in some snow showers in the upslope areas, but accumulations will be minimal. Snow showers should abate Monday as the gradient relaxes slowly and high pressure moves closer. Monday promises to be the coldest day so far this winter, with temps struggling to reach 20, and many places likely failing to do so. Monday night will also be cold, but with the high moving overhead, winds should slack off considerably, so wind chills likely won`t be nearly as bad. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Changeable weather expected through next week with very cold conditions early giving way to moderating temperatures with increasing precipitation mid-week, followed by falling temperatures again by the end of the week. Strong 1035-1040mb high pressure will be positioned overhead Tuesday morning, leading to near ideal radiational cooling conditions with morning lows likely bottoming out in the single digits and teens for many locations, with some sub-zero air temperatures likely. The air mass will however bounce in and out quite quickly, with south/southwest flow developing during the day Tuesday. Dry conditions still expected with highs rebounding in the 30s. The next system will then rapidly be moving through the eastern Great Lakes Tuesday night into Wednesday with its attendant cold front pushing eastward towards the region. This would place our region in the warm sector, with rain being the favored precipitation type on Wednesday. However as with any departing arctic air mass, there may be enough cold air to produce some freezing rain if precipitation can move in Tuesday night. Temperatures will then moderate further Wednesday. The most uncertainty then lies Wednesday night and Thursday as most model/ensemble guidance depicts secondary wave of low pressure riding along the frontal boundary near the region, although details to be determined. A secondary re-inforcing cold front will then move towards the area Friday with upslope snow showers possible. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... Low level wind shear will be a significant issue overnight along with rain, low clouds and low visibility. Rain ends very early Sunday with gusty winds, perhaps 40-45 knots, being the main issue most of the day. Highest winds in the afternoon. Winds lighten up slowly after that but otherwise remaining VFR Sunday night through Monday night. VFR expected for Tuesday with strong high pressure overhead. Potential for sub-VFR conditions then increases Wednesday into Thursday with widespread precipitation as next low pressure system moves into the area. Gusty southwest flow and low level wind shear may also become a concern Wednesday. && .MARINE... SCA remains in effect for the waters as low pressure crosses the region. Should then get very windy on Sunday as strong low pressure pulls away, so have gales for all waters. May need to extend gales into the night Sunday night and possibly Monday, then winds relax Monday night as high pressure moves overhead. Sub-SCA conditions expected Tuesday with high pressure overhead. SCA conditions then return Tuesday night through Thursday with increasing southwesterly flow ahead of the next low pressure system, turning northwest behind. && .TIDES/COASTAL FLOODING... Tides are elevated with onshore flow. Near minor flooding is possible through Sunday before strong northwest winds ensue. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Wind Advisory from 11 AM to 7 PM EST Sunday for DCZ001. MD...Wind Advisory from 7 AM to 7 PM EST Sunday for MDZ003-501-502. Winter Weather Advisory until 6 AM EST Sunday for MDZ003-004. Wind Advisory from 11 AM to 7 PM EST Sunday for MDZ004>006-011- 013-014-016>018-503>508. Winter Storm Warning until 6 AM EST Sunday for MDZ501-502. VA...Wind Advisory from 7 AM to 7 PM EST Sunday for VAZ025>031-503- 504-507-508. Wind Advisory from 11 AM to 7 PM EST Sunday for VAZ040-051>054- 501-502-505-506. Winter Weather Advisory until midnight EST tonight for VAZ507. WV...Wind Advisory from 7 AM to 7 PM EST Sunday for WVZ050>053-055- 501>506. Winter Weather Advisory until 6 AM EST Sunday for WVZ050>052- 055-501>505. MARINE...Small Craft Advisory until 6 AM EST Sunday for ANZ532>534-536- 537-540>543. Gale Warning from 6 AM to 6 PM EST Sunday for ANZ530>543. && $$ SYNOPSIS...RCM NEAR TERM...LFR SHORT TERM...RCM LONG TERM...MM AVIATION...MM/LFR MARINE...MM/LFR TIDES/COASTAL FLOODING...LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.