Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201428 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1028 AM EDT Thu Apr 20 2017 .SYNOPSIS...
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High pressure off the coast will move further east today. A cold front will drop into the Mid Atlantic Friday afternoon. Weak high pressure builds over the area Friday night before low pressure impacts the area Saturday night and Sunday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The early morning showers have dissipated. Cloud cover has also been rapidly eroding as subsidence briefly overspreads the area...with mostly sunny skies across much of the area. Mostly sunny skies should allow for a quick warm up...with afternoon highs near 80 across much of the region. Scattered thunderstorms are expected to develop over the higher terrain early this afternoon and then gradually push east through the afternoon into the evening. CAPE/shear parameter space supports general thunderstorms (e.g., MLCAPE ~600-900 J/kg...0-6 km EBS ~20-30 kts)...with perhaps a very brief and localized pulse-type thunderstorm. The higher shear totals (~30 kts by late afternoon) are mainly focused to our north across PA...but could slip into the northern tier of counties near the Mason-Dixon line by early evening. While still low probability, this area is the most likely to experience a stronger thunderstorm. Any thunderstorms should weaken shortly after sunset as instability wanes with the loss of daytime heating.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... Boundary appears to be hanging around right into the weekend. This will lead to extensive cloud cover from Thursday night right through Saturday. The better chance for rain looks to be during Saturday as low pressure forms over the TN Valley and progresses east during the late afternoon. Highs look to reach the low 80s over much of the area Friday, but with the extensive cloud cover/rain Saturday highs will only reach climb to the low/mid 60s. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Unsettled weather looking likely for much of the weekend and into next week. An area of low pressure will move from the lower Mississippi River Valley Saturday to the Mid-Atlantic/Southeast coastline by Sunday, tracking eastward along a baroclinic zone. There remains some discrepancies between model suites as to how far north/south the zone becomes established and therefore the low track and area of steadiest/heaviest rainfall, but the setup should be favorable for a period of overrunning rain Saturday into Sunday. Energy will likely be slow to depart the east coast in the Monday/Tuesday timeframe, and with low pressure possibly lingering offshore as high pressure builds into New England, this may promote onshore flow, cool temperatures, lingering clouds and chances for showers. By Wednesday, should see more of a southerly flow develop as a low pressure system moves through the Great Lakes. This should bring warmer temperatures, as well as the possibility for additional showers, especially west. Temperatures will be on the cooler side in the extended period, with highs likely holding in the 50s for much of the region Sunday with rain/clouds. Some improvement Monday/Tuesday, with highs generally in the 60s. Warmest day looks to Wednesday where 70s likely. Lows during this time period mainly 40s to around 50F. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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Conditions continue to improve this morning as skies clear and rain pushes east of the terminals. VFR expected at all sites through much of the day today. Scattered thunderstorms are possible this afternoon into the early evening...with brief flight restrictions and gusty winds possible. Low clouds and periods of rain Saturday night and Sunday will likely bring widespread sub-VFR reductions to both ceilings and visibilities. Low clouds and areas of light showers may persist into early next week.
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&& .MARINE...
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While gradient winds are expected to remain below SCA values today/tonight, scattered thunderstorms are possible this afternoon into early evening (especially over the Upper/Middle Tidal Potomac). Brief/localized gusty winds are possible in the strongest thunderstorms...with a chance for a few Special Marine Warnings. Rain is expected for the waters Saturday. Generally sub-SCA conditions expected Saturday night and Sunday. SCA conditions possible Monday with increasing northeasterly flow.
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&& .TIDES/COASTAL FLOODING...
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Water levels continue to decline...with tidal anomalies generally a half to three quarters feet above normal. Current forecast keeps all sites below action stage over the next several tidal cycles.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ UPDATE...MSE PRODUCTS...WOODY!/MJM

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