Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251837 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 237 PM EDT Thu Aug 25 2016 .SYNOPSIS...
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High pressure remains off the coast today. 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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Debris clouds from the overnight convective complex remain across the forecast area this afternoon, which has inhibited new convective development today. A composite of mesoscale guidance suggests that any development likely to be in/near the central foothills of the Blue Ridge before the end of the day. Based on current trends and recent HRRR runs, suspect that coverage may be widely scattered at best. Am still holding out hope for a limited area 30 PoP for a couple hours near the end of the day in the aforementioned area. Clouds may end up being the most noticible sensible weather feature this afternoon. Additional thunderstorms will be developing in northeast Ohio/northwest Pennsylvania late today. Some of that may slip into the Potomac Highalnds before dissipating tonight, somewhere near midnight.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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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.
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&& .LONG TERM /SUNDAY THROUGH THURSDAY/...
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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.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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VFR conditions will prevail for the current TAF period. Plenty of mid-high level moisture from convective debris providing the ceiling, but lower cumulus forming near FL050. The mix of clouds should carry through much of the night, inhibiting clouds. There are small chances of thunderstorms, especially near CHO late today and MRB late this evening. Odds of a direct impact of any storm remain slim. 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 surpressed. High pressure will return for the weekend. VFR should prevail.
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&& .MARINE...
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Status quo on the waters. We`re in a marginal Small Craft Advisory environment on the waters. Will keep the SCA in place through the evening. A weak front will slide through on Friday. Flow will veer west Friday morning, northwest Firday evening, and eventually becoming east by late Saturday, as high pressure moves to the north. At this time, sub- SCA conditions expected.
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&& .TIDES/COASTAL FLOODING...
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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. Have low confidence in Annapolis reaching minor flood (if it does, it will be a threshold Advisory for a couple of hours), so have opted to not raise Advisory at this time. Winds will become west Friday and north by early Saturday. There should not be any concerns beyond tonight`s cycle.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ531>533- 539>541. Small Craft Advisory until 6 AM EDT Friday for ANZ534-543. && $$ SYNOPSIS...RCM/HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...IMR AVIATION...HTS MARINE...HTS TIDES/COASTAL FLOODING...HTS

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