Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211904 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 304 PM EDT Wed Mar 21 2018 .SYNOPSIS... Low pressure east of the Delmarva Peninsula will move northeast to a position near Cape Cod on Thursday morning. High pressure will build across the region tonight through Saturday. Low pressure over the mid-Mississippi Valley on Saturday will move east across the Carolinas on Saturday night. High pressure will build across the mid-Atlantic Sunday through Monday. && .NEAR TERM /THROUGH TONIGHT/... At 1830Z, regional radar mosaic shows decreasing trend in reflectivity across the CWA, with the core of banding directly over the mid-to-northern Chesapeake Bay. This morning`s 12Z NAM, GFS, and ECMWF all show at most a few tenths of an inch QPF through mid- evening, therefore at most 1-3 inches additional snowfall forecast. The high end of these accumulations will be primarly northeast of Baltimore in northern Baltimore and Harford Counties. Scattered light snow showers can be expected this evening CWA-wide, before tapering to flurries overnight. Areas west of the Blue Ridge should be snow-free after midnight tonight. Tonight low temperatures will be below freezing across the entire CWA, with the exception of locations directly adjacent to the Chesapeake and tidal Potomac. Even expecting temps to drop at or below 30F in the cities of Baltimore and Washington. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Skies are forecast to be partly cloudy by mid-morning Thursday across much of the CWA, and continue to become less cloudy through Friday night. With the sunshine, high temps will be in the lower 40s both Thursday and Friday, but with a 20-30 mph gusty northwest wind with mixing during the daylight hours. Thursday night and Friday night lows will drop to the mid 20s, under the influence of clear skies && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... High pressure centered over Canada will be in control on Saturday before a quick moving low pressure system dives from the Mid-Mississippi Valley and reaches our area Saturday night into Sunday. Guidance suggests that the best chance of precipitation will be to the southwest of our CWA in the form of snow. The high pressure system over Canada will build over our region late Sunday, move southward on Monday and settle overhead on Tuesday. Another low pressure system will approach mid-week. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... BWI and MTN will continue to have IFR, with LIFR at times, through the remainder of the afternoon. All other terminals primarily IFR through late this afternoon, with improving conditions to MVFR early this evening. Gusty NW winds return late tonight and Thursday to all terminals. VFR conditions expected on Saturday, before another system may affect us Saturday night into Sunday with possible sub- VFR conditions. VFR conditions return later on Sunday into Monday. && .MARINE... SCA winds are expected overnight on the big waters of the Tidal Potomac below hte US 301 bridge and Chesapeake, and then spread to all waters on Thursday. This nocturnal cycle will repeat through Friday, when SCA conditions are once again expected. Wind gusts will be below SCA criteria on Saturday and remain below through Sunday, but still breezy. Winds will be near or above SCA criteria on Monday. && .TIDES/COASTAL FLOODING... We continue in the battle between northerly winds and the lower Bay surge from the coastal storm. This is leading to virtually zero anomaly in the upper Bay and over a foot and a half above normal tide in the southern Maryland Bay. The result of this is continued minor flooding of sensitive areas in St. Mary`s County, Maryland with high tide this afternoon/evening and early Thursday morning. Once the coastal low pulls away, the northerly winds will totally win out with decreasing tide levels. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Winter Storm Warning until 8 PM EDT this evening for DCZ001. MD...Winter Storm Warning until 8 PM EDT this evening for MDZ003>006-011-013-014-016>018-501>508. Coastal Flood Advisory until 9 AM EDT Thursday for MDZ017. VA...Winter Storm Warning until 8 PM EDT this evening for VAZ025>031-036>040-050>057-501>508. WV...Winter Storm Warning until 8 PM EDT this evening for WVZ050>053-055-501>506. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ530>534- 537>543. Small Craft Advisory from 8 PM this evening to 6 PM EDT Thursday for ANZ535-536. && $$ SYNOPSIS...Lee NEAR TERM...Lee SHORT TERM...Lee LONG TERM...IMR AVIATION...Lee/IMR MARINE...Lee/IMR TIDES/COASTAL FLOODING...JE is the U.S. government's official web portal to all federal, state and local government web resources and services.