Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 260424 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1224 AM EDT Fri Aug 26 2016 .SYNOPSIS... High pressure remains off the coast through tonight. A cold front will cross the region early Friday. High pressure will return for the weekend. Another front may slowly slide southward into the area by the middle of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... High pressure will remain offshore tonight and a weak surface trough will remain overhead. A light southerly flow will allow for noticeably warmer and more humid conditions overnight compared to recent nights. Min temps will range from the mid to upper 60s in the Potomac Highlands and portions of the Shenandoah Valley to the middle 70s near Washington and Baltimore. A cluster of showers and thunderstorms have developed ahead of a cold front over Pennsylvania this evening. This activity will slowly build south and east toward northern Maryland overnight. Current feeling is that the activity will weaken as it approaches our area due to the fact that it will be outrunning the cold front that will not get here until after sunrise...and there will be less instability due to the loss of daytime heating. Will have to monitor this though...because with dewpoints in the 70s there will be some instability hanging around through the night. Will continue with slight chance/chance for showers and isolated thunderstorms across our northern and western zones overnight. Patchy fog is expected overnight as well due to more low-level moisture in place and light winds. Fog should be confined to favored areas in river valleys and rural areas...but fog may be locally dense. && .SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY NIGHT/... Timing of the surface boundary continues to inch earlier. Consensus timing looking like daybreak-mid morning from northwest to southeast. Based on this timing, believe the passage will be dry. Not only is the timing out of synch with favored diurnal trends, but west/northwest winds will promote subsidence, and at all levels above the surface ridging will reinforce that subsidence. The downslope flow may take the edge off the humidity but compressional warming may add to the temperature instead. Will await the 12z ECMWF before deciding tomorrow`s temperature. Ridging will keep muggy but rain-free conditions in place Friday night through Saturday night. Temperatures won`t stray far from an ensemble blend. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Ridge of high pressure aloft sits over our region Sunday while a frontal boundary slowly approaches Sunday night into Monday. This boundary will remain near or over our CWA Monday into Tuesday bringing a chance of showers and thunderstorms. Shortwave energy moves near our CWA Tuesday night and forecast becomes uncertain after this. Moisture advection will be affecting our area but depends on which guidance is used, the source/wind direction varies. But in general... showers and thunderstorms are possible Wednesday and Thursday. The forecast will be refined as confidence increases. Temperatures will be in the mid 80s and low 90s and heat indexes in the mid 90s. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/...
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A weak boundary will slip across the terminals Friday morning, veering winds west (around 10 kt). These winds will eventually be northwest by the end of the day. Most moisture will mix out and any additional clouds will be suppressed. High pressure will return for the weekend. VFR should prevail.
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&& .MARINE... Status quo on the waters. We`re in a marginal Small Craft Advisory environment on the waters. Will keep the SCA in place into the overnight. A weak front will slide through on Friday. Flow will veer west Friday morning, northwest Friday evening, and eventually becoming east by late Saturday, as high pressure moves to the north. At this time, sub- SCA conditions expected...but wind gusts may be close to SCA criteria Friday due to a deep mixing layer. Have capped gusts around 15 knots for now since there will be a weak gradient but it will be close. && .TIDES/COASTAL FLOODING... Water levels about a half-foot above astronomical norms. ESTOFS depicting its typical water piling in the northern extent of the Bay. Some of this is a model bias. Believe that caution stages will be reached. Still have low confidence in Annapolis reaching minor flood but it will be close (if it does, it will be a threshold Advisory for a couple of hours). Therefore...have not issued an advisory at this time. Winds will become west Friday and north by early Saturday. There should not be any concerns beyond tonight`s cycle. && .CLIMATE...
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Ranking of summer 2016 in terms of average temperature (JUN 1 - AUG 24) Site RankAverage Temperature DC 4 80.4 Balt 23 (tie with 3 other years) 77.2 IAD 3 77.2 .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 2 AM EDT early this morning for ANZ531>533-539>541. Small Craft Advisory until 6 AM EDT early this morning for ANZ534-543.
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