Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 170759 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 359 AM EDT Sun Sep 17 2017 .SYNOPSIS...
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Warm high pressure will remain over the eastern United States this week. Meanwhile, Hurricane Jose is expected to track north off the coast of the eastern United States during the early to mid week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Surface high pressure resides atop the northeast and Mid Atlantic regions early this morning. Most of the scattered mid-level cloud cover that survived past midnight has since dissipated. With nearly clear skies, no wind, and dewpoints well into the 60s, the environment has been favorable for fog formation. Its becoming more than localized, and have switched to areal wording. Thus far (as of 3am) no dense fog has been noted. However, NARRE/HREF/GLMP have been suggesting that an area of low clouds/fog present across the Delmarva and Virginia tidewater will be spreading west to near I-95 by dawn with a good (70-90%) probability of fog less than 1/2 mi. Based on the current situation, that may be a pinch overdone. Am leaning forecast in that direction, but any statement or advisory will likely be a game-time decision. Once the low clouds and fog burn off...which likely will be by mid- morning...the atmosphere will be similar to the past couple of days. Anticipate cumulus to develop during the afternoon, with widely scattered showers soon thereafter. Uninhibited CAPE does support the precipitation, but shear, lapse rates, and a synoptic source of lift are all lacking. Thus PoPs will be highest in the mountains. Once again believe that NAM/GFS/ECMWF are overdoing QPF output, and am siding closer to CAMs. Temperatures will likely be fairly close to yesterday, and am taking cues not just from ensemble MOS but also persistence.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/...
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Since there will be little change in air mass through Monday, with plenty of moisture and rather low mid-level heights, the forecast will be fairly similar through the period. The challenges will be fog development tonight, especially late at night, followed by diurnal development during the day. The fog will be dictated by where residual clouds reside; have broad-brushed the potential pretty much areawide. As for precip, Jose will be offshore but nearing the Mid-Atlantic by late Monday. While the system likely won`t be affecting the area directly, onshore flow will add to the low-level moisture profile as well as enhancing convergence. Therefore it will be harder to pinpoint where showers may or may not be. Have a 20-30 PoP just about anywhere during the afternoon. Jose`s track most likely will be far enough offshore to preclude impact as it makes its pass Monday night into Tuesday. Only minor PoPs remain in the Bay and adjacent zones. Do have some cloud cover though. While track errors will be less as the cyclone nears, and model guidance is in good agreement, changes are still possible. Please refer to the National Hurricane Center for updates on the forecast regarding Jose.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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The track of Jose becomes very uncertain for the late week, although the potential for significant impacts here is low. Also tropical storm Maria will be the next system to watch for potential U.S. impact next week. Those two Atlantic tropical systems and high pressure over the eastern United States will be the main weather features of note through this upcoming weekend.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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Flight restrictions will be a challenge at the start of the period. NARRE/LAMP/HREF all suggest that IFR (or lower) will march west, stopping at DCA/BWI by sunrise. Suspect this will more of a low cloud issue vs fog, but there will be some of both. Outside of this, areas of fog are developing. Presently am holding onto MVFR, but predominant IFR probable at MRB. Brief IFR (or lower) possible just about anywhere, but confidence in specifics low. Assuming the cloud back does spread west, is dissipation will be the next challenge. Sun angle not as strong as it would be mid-summer, but we should be able to get back to VFR by mid-morning. Scattered showers possible this afternoon. Coverage in doubt, and any impact would be limited and brief. Am keeping VFR in the forecast. Tonight and tomorrow will be a carbon copy with respect to concerns, ie: fog to start the day followed by widely scattered afternoon showers. Once again, Flight restrictions likely in low clouds and fog, but confidence in details low. Jose will make its nearest pass in its northbound trek Monday night and Tuesday. Impacts should remain east of the terminals, based on the current forecast. Past that, only aviation concern thru Thu is the potential for patchy morning fog.
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&& .MARINE...
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Winds light, and should remain so into Monday. The gradient increases thereafter as Jose nears the waters. The cyclone will remain well offshore as it heads north Monday night and Tuesday. Small Craft Advisories does appear likely during this time. Gale not out of the question, but its a rather low probability event at this point. Past that, no significant marine concerns through Thu.
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&& .TIDES/COASTAL FLOODING...
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Water levels running about a half-foot above astronomical normals, but that is sufficient to touch minor flood threshold at St George Island. Elsewhere, caution stages have been met at many sites. Without much flow, suspect the result will be same during the daytime tide cycle today. Water levels will then start to inch upward as Jose nears the mouth of the Chesapeake and forces water into the estuary. There is a wide range of solutions as to how extensive this rise will be. The nighttime tide cycle is astronomically preferred. Depending on how close the storm gets, moderate is not impossible, but uncertainty on this is very high at the moment. Based on confidence, have extended the Coastal Flood Advisory for St Marys County for two more cycles. It likely will need to be continued beyond that. No other actions have been taken at this point, but Annapolis may be at risk for minor flooding Sunday night/early Monday morning.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory until 3 AM EDT Monday for MDZ017. VA...None. WV...None. MARINE...None.
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&& $$ SYNOPSIS...CAS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...CAS AVIATION...HTS/cs MARINE...HTS/cs TIDES/COASTAL FLOODING...HTS

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