Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 250751 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 351 AM EDT Tue Oct 25 2016 .SYNOPSIS... High pressure will remain over the region through midweek. A cold front will cross the area Thursday afternoon and evening. High pressure returns Friday and Friday night. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Surface high pressure ridge still resides across the western Great Lakes and Midwest. In spite of the pressure gradient across the Northeastern United States, the central Shenandoah Vally has managed to partially decouple...most notably at SHD and 8W2 where temperatures already in the mid 30s. For that reason, believe the Frost Advisory for the Valley looks good. West of there, its more iffy, but colder conditions likely in the deeper valleys. Therefore, Frost/Freeze still has a chance at verifying. In spite of building high pressure today, there will be enough of a pressure gradient to support breezy conditions, particularly across Maryland. Model soundings support gusts around 20 kt. Cyclonic stratocumulus clouds evident on satellite at this time in the Appalachians and across Pennsylvania. Believe that will continue through the morning. The cloud layer may thin in the afternoon, but there is still respectable saturation near the LCL. Forecast high temperatures seem to be on track. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/... The high pressure ridge sits overhead tonight. Dry air and calm winds suggest near ideal radiational cooling conditions, and forecast low temperature below guidance. However, there is a complication, in the form of return warm air advection present across central Virginia by midnight. Therefore, am not confident on how much will be a freeze vs. a frost. Believe there is time to sort that out, as well as the state of the growing season after this morning. Therefore have opted to keep the Freeze Watch in place for now instead of making the warning/advisory decision. Nonetheless, it will be a cold night, and areas of frost will be common. Warm advection may not effectively mix to the surface until the ridge axis exits to the east. That won`t be until Wednesday night. Therefore, Wednesday`s high temperatures will be comparable to today, if not a pinch cooler. The Thursday morning low, on the other hand, will be significantly warmer. There is decent model agreement in tracking low pressure from Iowa/Missouri on Wednesday to near Lake Erie on Thursday. That will keep the bulk of the upglide/vorticity forcing north of the forecast area. Have scaled back POPs (20-30%) until early Thursday morning for only the Potomac Highlands and Martinsburg-Hagerstown area. Still believe that likely POPs prudent across the north on Thursday, chance POPs elsewhere. The passage of the attendant cold front Thursday afternoon will be the primary forcing mechanism. && .LONG TERM /FRIDAY THROUGH MONDAY/... Post-frontal conditions are expected Friday as high pressure moves into the region. Dry and cool conditions are expected with temperatures reaching the U50s/L60s in most places. High pressure moves overhead Friday night through Saturday before a warm front advances northward from the Ohio Valley. Isolated to scattered showers are possible Saturday however most activity should stay north of Maryland. Low pressure will move across the northern Great Lakes Saturday night into Sunday and an associated cold front will likely slowly move southward from north to south Sunday and rain showers are possible into Monday. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... VFR conditions anticipated for the valid TAF period under building high pressure. Northwest winds will still gust to 15-20 kt upon diurnal mixing today, but winds will become light tonight upon sunset. VFR conditions Wednesday under high pressure. Flight restrictions possible Thursday due to low clouds/showers as a cold front crosses area. Periods of MVFR seem most plausible at this time. VFR likely Friday into Saturday. && .MARINE... Winds have partially decoupled overnight, but occasional Small Craft Advisory conditions ongoing on most of the Bay and lower tidal Potomac. Upon sunrise believe that mixing will improve. Atmosphere will still support 20 kt gusts. As such, SCA continues on all waters today. Have extended SCA into tonight for the Bay and lower Potomac based on guidance continuing a mixed atmosphere over the waters. Winds will be much lighter by Wednesday morning as the ridge axis will be overhead by that time. Return flow will hold off until Wednesday night, and that will be from the east/southeast. Southerly gradient returns during the day on Thursday, perhaps up to 15-20 kt again. Small craft conditions, in northwest flow, may continue into Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Freeze Watch from late tonight through Wednesday morning for MDZ003>006-501-502-507. VA...Freeze Watch from late tonight through Wednesday morning for VAZ026>031-503-504. Freeze Warning until 9 AM EDT this morning for VAZ503-504. Frost Advisory until 9 AM EDT this morning for VAZ025>027-029. WV...Freeze Watch from late tonight through Wednesday morning for WVZ050>053-055-501>506. Freeze Warning until 9 AM EDT this morning for WVZ505-506. Frost Advisory until 9 AM EDT this morning for WVZ055-501-502. MARINE...Small Craft Advisory until 3 AM EDT Wednesday for ANZ531>534- 537-539>543. Small Craft Advisory from 9 AM this morning to 6 PM EDT this evening for ANZ530-535-536-538. && $$ SYNOPSIS...HSK NEAR TERM...HTS SHORT TERM...HTS LONG TERM...HSK AVIATION...HTS MARINE...HTS is the U.S. government's official web portal to all federal, state and local government web resources and services.