Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250130 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 930 PM EDT Sat Sep 24 2016 .SYNOPSIS... High pressure will build in for tonight and Sunday before moving off the coast Monday. A cold front will pass through the area overnight Monday into Tuesday. An upper-level low may impact the area during the middle portion of next week. && .NEAR TERM /THROUGH SUNDAY/... Exact location of cold front is difficult to pinpoint this evening due to diffuse surface features, but is likely toward southern VA. A secondary boundary resides over PA, behind which dew points are in the mid 40s. The boundary will make some inroadsacross northeastern sections of the CWA tonight. A couple of small isolated showers remain near the central Blue Ridge, and these should dissipate/push southeast in the next couple of hours. Based on model RH fields, the clearing line is nearing its southern extent for the night. This low level moisture and onshore/upslope flow may result in some patchy drizzle and fog for the southern third of the CWA tonight. These features may hold low temperatures in the 60s. Further north, clearing skies, decreasing winds, and lowering dew points should result in the coolest night of the season thus far, with 50s widespread and 40s in the colder/northern locales. On Sunday, high pressure drifts by to the north and flow becomes more easterly. Temps will rebound only into the lower 70s in most areas due to cool air aloft in northern areas and persistent clouds further south. Some drizzle/mist may linger in central Virginia during the morning. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... High pressure continues drifting eastward away from us Sunday night and Monday as the next frontal boundary approaches from the west. With persistent east/southeast flow the available moisture will increase and the front may be slow enough and forcing strong enough to allow for a decent rain across the area Monday night into early Tuesday. Right now guidance is a bit uncertain on exact timing but certainly Monday night looks wet...with uncertainty on just how fast it arrives late Monday and how fast it departs Tuesday. Lows will be cool again Sunday night (50s to high 40s) with highs Monday as the front approaches again stuck in the lower 70s. Monday night will be milder with the front crossing the area, with lows staying in the 60s for many spots. Clouds breaking Tuesday will likely allow for 70s to return once again. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Cold front moves away from our region Tuesday night, with some showers possibly lingering to the eastern part of our CWA. Conditions become dry overnight Tuesday into Wednesday. A cutoff upper level low will push south from the Great Lakes Wednesday into Thursday night or even late Friday. Guidance is in disagreement on location of this upper level low and this will affect the forecast in the long term. GFS keeps the upper low moving over the Mid-Atlantic early on Thursday with the ridge building behind it on Friday and northerly flow through early Saturday. This scenario brings showers over our CWA Wednesday night into Thursday, and then dry into Sunday. On the other hand, the Euro keeps the upper level low to our west and lingering to our southwest through early Friday before moving back north. This scenario allows for southerly or easterly flow advecting moisture into our region and bringing precipitation chances Wednesday night into Saturday before finally drying out late Saturday into Sunday. Temperatures will be affected by the position of the upper lever low, but for now forecasting near normal. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... Clouds have mostly cleared away from the northern terminals, but recent obs of FEW015-025 at DCA/BWI lend some concern that clouds may try to redevelop. This hasn`t been indicated in guidance, so have left out of the TAFs for now. Low level moisture reaching CHO this evening, and cooling overnight should allow MVFR cigs. Kept these cigs through 12Z due to climo, disregarding guidance showing improving conditions overnight. Could also be some patchy mist or drizzle around CHO later tonight. Generally VFR Sunday-early Monday, although low cigs could be a concern at CHO again Sunday night. Then sub-VFR with approaching front and associated SHRA Monday night into early Tuesday. Winds generally around 10 knots or less through Tuesday...starting off northeasterly tonight...turning southeasterly Sunday...and southerly Monday...then westerly Tuesday. VFR conditions expected Tuesday night into Wednesday, then sub- VFR conditions possible late Wednesday into Friday as upper level disturbance brings showers into the region. && .MARINE... Other than a stray 20 kt gust around Pt. Lookout, winds have been sub-SCA this evening. A secondary boundary pushing southward and cool air advecting over the warm bay waters could result in a surge of winds on the northern part of the Bay after midnight, so have left SCA in effect and extended until 10 AM based on hi-res guidance. However, it looks rather marginal. Trimmed the SCA for the southern MD waters back to 2 AM however, as no guidance shows the stronger surge of winds reaching these waters after the gust potential diminishes this evening. High pressure likely to bring lighter winds Sunday before southerly channeling ahead of cold front bring another threat of SCA for Monday and then cold advection brings more potential SCA gusts Tuesday behind aforementioned front. Winds diminish Tuesday night into Wednesday night. Possible small craft advisory conditions late in the week an as upper level disturbance moves nearby. && .TIDES/COASTAL FLOODING... High pressure building southward just to the northeast of the area will result in northeasterly flow through tonight, then easterly to southeasterly flow late Sunday into early next week. Anomalies have dropped some this afternoon, but the overall pattern will not allow much more water to drain out of the Chesapeake Bay/Tidal Potomac River. Anomalies will likely begin to increase again starting later tonight. Minor coastal flooding appears possible by the Sunday night high tide cycle. && .CLIMATE... Unusually warm weather has persisted over the area for quite some time. Autumn-like temperatures are finally making an appearance over the area, and DCA may fall below 60 degrees early Sunday morning for the first time since June 9th (total of 106 days through September 23rd). The record most consecutive days at or above 60 degrees in the Washington DC area is 112 set in 2012. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 10 AM EDT Sunday for ANZ530>533- 538>541. Small Craft Advisory until 2 AM EDT Sunday for ANZ534-537-543. && $$ SYNOPSIS...RCM NEAR TERM...ADS/RCM SHORT TERM...RCM LONG TERM...IMR AVIATION...ADS/IMR/RCM MARINE...ADS/IMR/RCM TIDES/COASTAL FLOODING...DFH CLIMATE...DFH

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