Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 180737 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 337 AM EDT Mon Sep 18 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 Mid Atlantic coast tonight through Wednesday. Refer to the National Hurricane Center`s website hurricanes.gov for the latest on Jose.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A ridge of high pressure extends from New England down the eastern seaboard early this morning. A mid-level ridge extends up the Appalachians. This tandem will lead to subsidence across the area. Before we get there though, we`ll need to address early morning low clouds and fog. There is still a fair amount of mid level clouds across the area though, which is keeping fog localized. Like last night, a bank of low clouds can be found across the Atlantic coast, and NARRE/HREF suggest they will work inland again. Believe that low clouds will dominate over fog given light but present flow. Nonetheless, this will lead to a gray start to the day. Eventually, the low-level moisture will burn off, but it may take some time to do so. The relative lack of strong insolation, dry air aloft, the lack of any shear, and subsidence (as already mentioned) should combine to prevent showers today. The best chance (relatively speaking) will be in the mountains where orographics and convergent onshore flow will provide minimal lift. It will be plenty humid for the season, as the northeast wind will assist dewpoints in reaching 70 degrees. Temperatures will be about the same...around 80 degrees.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
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By tonight, the forecast will begin to be influenced (indirectly) by Jose, although the bigger influence (again, relatively speaking) will be felt on Tuesday. Northeast/north winds will increase tonight, especially near the Bay, with a fair amount of cloud cover east of the Blue Ridge as well. Will be bringing a chance of showers inland to the western shore by dawn Tuesday, with better chances during the day on Tuesday. The inland reach of these showers likely won`t spread west of I-95, but that is an aspect that is highly conditional on the track of Jose, as well as how much the storm expands as it weakens. A slight nudge westward would increase the potential that an outer band could spread inland, providing a soaking rain. Am still keeping a solution of subsidence in the wake of the cyclone, which will affect the forecast area Tuesday night and Wednesday.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/...
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Ridge of high pressure surface and aloft will build over the region Thu through Sun as Jose remains well offshore. Tranquil conditions are expected as a result. Temperatures will remain a few degs above normal during this period. By early next week, the ridge begins to weaken as a weakening post- tropical Jose likely completes another loop and heads back to the mid-Atlc coast. We`ll also be watching Hurricane Maria move into the southwest Atlc during the second half of the week. Recent trends indicate Maria may stay out to sea, but it is really too early to tell at this time. Please refer to NHC for the latest on Jose and Maria.
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&& .AVIATION /08Z MONDAY THROUGH FRIDAY/...
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Once again, low clouds and fog are a concern for the morning push. Unlike last night, there is a bigger contribution from mid clouds, which is disrupting fog formation processes. Some guidance again is providing high probabilities that low clouds will spread inland to BWI and perhaps DCA. The odds aren`t as high as last night, and the cloud deck is further removed from the area. However, the solution is plausible. Have forecast IFR only at BWI; have kept cigs 010-015 DCA/IAD. Whatever does develop will slowly burn off through the morning. VFR will prevail for the balance of the day. Jose will make its nearest pass to the terminals late tonight through Tuesday. Significant impacts will likely remain to the east, but northeast winds tonight suggest there may be another round of low clouds to deal with. VFR should prevail Tuesday afternoon through Friday, aside from perhaps early morning fog.
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&& .MARINE...
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Although winds are weak early this morning, the pressure gradient will be increasing today and tonight as Jose nears the waters.The current alignment for Small Craft Advisories this afternoon and tonight still appear on track; no changes were made there. By Tuesday, the gradient will be at its strongest, with several model solutions suggesting the gales will be possible on the mid Bay. That is contingent on the track of Jose. Have added a Small Craft to all Maryland and DC waters on Tuesday since confidence in 20+ kt gusts high. Would not rule out an upgrade to Gale Warning for a portion of this area. Winds should stay generally below SCA Wednesday through Friday under ridge of high pressure.
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&& .TIDES/COASTAL FLOODING...
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Water levels continue less than a foot above astronomical predictions. This trend should gradually increase over the next couple of days. At this point, St George Island will be the only site forecast to consistently exceed minor flood, although Annapolis and SW DC will come precariously close. Have added a short-fused Coastal Flood Advisory for Anne Arundel county for the next couple of hours. May need to do the same for SW DC for the early morning. Otherwise, just caution stages with the current tide cycle. Based on strong confidence in the trends, have extended the Advisory for St Marys County for another three tide cycles, through the daytime cycle Tuesday. Elsewhere, model spread precludes action at this time. While moderate flood possible at sensitive locations, confidence in this outcome at the low end of the spectrum. Elevated water levels likely to be a concern through the end of the week.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory until 7 AM EDT this morning for MDZ014. Coastal Flood Advisory until 4 PM EDT Tuesday for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory from midnight tonight to 8 PM EDT Tuesday for ANZ531-532-539-540. Small Craft Advisory from 6 AM to 8 PM EDT Tuesday for ANZ530- 535-536-538. Small Craft Advisory from 6 PM this evening to 8 PM EDT Tuesday for ANZ533-541-542. Small Craft Advisory from 3 PM this afternoon to 8 PM EDT Tuesday for ANZ534-537-543.
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&& $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...LFR AVIATION...HTS MARINE...HTS/LFR TIDES/COASTAL FLOODING...HTS

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