Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250156 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 856 PM EST Wed Feb 24 2021 .SYNOPSIS... A cold front will pass through the area tonight and high pressure will build in behind the boundary through Friday. A multi-low system will impact the region late Friday and through this weekend. High pressure returns for early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... A cold front that extends from western Maryland through West Virginia this evening will continue to drop south and east, passing through our area tonight. A few showers are expected in the Allegheny Highlands, and perhaps into eastern West Virginia, western and north-central Maryland, and the northern Shenandoah Valley. However, dry conditions are most likely to persist farther southeast as the boundary outruns the upper- level support well to our north. Having that been said, a sprinkle or stray shower cannot be completely ruled out, but confidence is too low to introduce into the forecast at this time. A southwest flow has allowed for unusually mild conditions this evening. However, a northwest flow overnight will bring a return of more seasonable temperatures along with gusty winds. Bumped up wind speeds overnight to gust around 25 to 40 mph behind the boundary. Latest bufkit guidance does show a small stable layer near the surface, which would keep the strongest winds over the ridges. However, given the cold and dry advection combined with the pressure rises, latest thinking is that these winds will make it into the valleys and Wash/Balt metro areas as well. Therefore, the latest forecast has been updated to reflect that, with the strongest winds over the northern and central portions of the CWA where the pressure surge behind the cold front will be strongest. Precipitation may change to scattered snow showers along and west of the Allegheny Front before ending late tonight. Any snow accumulation will be light, but with temps falling below freezing there may be slippery areas by the morning along the ridges. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... The cold front will pass southeast of our region by early Thursday morning. Behind the frontal passage, winds will become west to northwesterly leading to advection of cooler and drier air into our region. Skies will become mostly clear with cooler afternoon temps in the mid to upper 40s to low 50s. Overnight lows will be chilly in the 20s and lower 30s. High pressure will build into our region Thursday afternoon and remain situated over the region through Friday. Temperatures will moderate through this period with near normal temps in the upper 40s to lower 50s. The high pressure overhead and will shift eastward off the eastern seaboard Friday afternoon. A multi low frontal system will pass to the south of our region late Friday and into Saturday. A coastal low will form along this frontal system and move north into our region on Saturday. The initial precipitation associated with this system will impact our region early on Saturday morning. Wintry precipitation during the initial onset (especially near the Mason-Dixon Line and along the ridges) is possible, but the high pressure becoming situated off the coast will lead to a east to southeasterly flow which will advect in warmer and more moist air into our region and limit below freezing conditions. Therefore, confidence for wintry precipitation in the valleys lowers. Overnight lows will hover in the 30s with near freezing temps mainly along the Allegheny front and along the ridge tops in the Potomac Highlands and Blue Ridge Mountains. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Wet weather appears in store for Sunday and Mon as series of upper level disturbances move across the region north of a stationary front along the NC/VA border. There could multiple periods of rain or repeated activity as front remains stationary, but lack of instability suggests rain will be stratiform limiting rainfall rates, and thus, potential for any flooding. EPS reasonable worst case scenario is for amounts ranging from an inch across the north to inch and half across the south. High pressure builds for Mon night before another low pressure impacts the area next Wednesday. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... A cold front will pass through the terminals tonight. Strong northwest winds are likely to develop behind the boundary with gusts around 25 to 30 knots (with even a few gusts around 35 knots possible). The strongest winds are expected after 02z at KMRB, and after 05z across the rest of the terminals. Gusty winds will continue into Thursday morning before diminishing later Thursday as high pressure draws closer. High pressure will bring VFR conditions through Thursday night. A brief period of VFR overcast conditions will be possible Friday morning as an upper level jet passes overhead. Winds will become east to southeasterly on Friday with gusts of 10 to 15 knots. Flight restrictions likely Sunday into Monday. && .MARINE... A south to southwest flow will continue through this evening with a few gusts near SCA criteria. However, a cold front will pass through the waters overnight, and strong northwest winds are expected behind the boundary. Frequent gusts around 25 to 30 knots are expected (especially after 05z from northwest to southeast). An SCA is in effect for all of the waters. Gale force gusts are possible during this time, but confidence is too low for a Gale Warning since the strongest wind field aloft will occur when air temperatures are still a little warmer than the water temperatures (despite cold advection). This will have to be monitored closely because a Gale Warning may be needed briefly overnight. Winds will gradually diminish Thursday as high pressure draws closer. SubSCA conditions likely Thursday evening into Friday. SCA conditions do not appear likely as area remains stable north of a surface front. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 11 AM EST Thursday for ANZ531-538- 539. Small Craft Advisory until 1 PM EST Thursday for ANZ532>534- 537-540>543. Small Craft Advisory from 1 AM to 11 AM EST Thursday for ANZ530-535-536. && $$ SYNOPSIS...JMG NEAR TERM...BJL/JMG SHORT TERM...JMG LONG TERM...LFR AVIATION...BJL/LFR/JMG MARINE...BJL/LFR/JMG is the U.S. government's official web portal to all federal, state and local government web resources and services.