Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 241840 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 240 PM EDT Sun Sep 24 2017 .SYNOPSIS... High pressure will remain in place through the first part of the week, then slowly weaken its grip over the area by the midweek as Hurricane Maria moves northward through the Western Atlantic. A cold front will move through late in the week, bringing more seasonable temperatures. && .NEAR TERM /THROUGH TONIGHT/... High pressure across the Great Lakes extends down into the Mid Atlantic this afternoon. A few cumulus clouds seen on visible satellite across the ridge tops, which should dissipate upon sunset. With full insolation under the ridge, DCA along with a couple of other sites have reached 90 degrees. Dewpoints in the lower to mid 60s should set the stage for tonight, as skies should remain clear and winds will be light. Low temperature forecasts follow this cue, with perhaps lows closer to 70 in the inner cities. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Locally, the synoptic pattern will remain similar through Monday and Tuesday. Maria turns in the western Atlantic, nearing the Outer Banks on Monday night, while the ridge overhead becomes pinched. The only implications to the forecast will be the extent of clouds spreading inland, and whether there will be sufficient moisture for any precip. At this point, clouds look likely Blue Ridge or I-81 east Monday night into Tuesday. Precip looks iffy...perhaps enough for a 20-30 PoP east of I-95. Of course, track changes would lead to changes in these details, so monitoring Maria`s progress via NHC would still be wise. Monday will still be a warm day. The thermal structure may be a degree or so cooler. By Tuesday, thicknesses will be lower and insolation less, supporting highs around 80 degrees east of the Blue Ridge. Since dewpoints will be the same, low temperature forecasts will be rather constant through the period. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... First part of the long term period will be determined by Hurricane Maria. Guidance suggests that Maria will be hovering just off of the North Carolina Outer Banks Wednesday into Thursday. This could somewhat increase winds over the southeastern portion of our CWA, but not expecting them to be particularly strong, maybe some gusts around 30 mph range in southern MD and over parts of the bay, Some showers from outer rain bands possible as well. The rest of our CWA can expect less impacts as we will remain in a warm air mass. Upper trough and its associated cold front should push the hurricane eastward away from the coast Thursday into Friday. This cold front will put an end to our above normal temperatures for late September and a more seasonable air mass will arrive behind it sometime Thursday or Friday. The fropa doesn`t look that moist, so expecting just some showers with it. Another -weaker- cold front approaches on Saturday and high pressure builds behind it into Sunday. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... VFR flight conditions will prevail through most of the valid TAF period, with a few wisps of cirrus, and perhaps a few cumulus as well during peak heating. Early morning fog possible Mon and Tue, clipping MRB and CHO. Have kept that risk in the TAF at MVFR. Will also need to watch for low clouds sneaking inland Monday night-Tuesday morning. Clouds will be more prevalent Tuesday. Flight restrictions possible, depending on what advects inland that early morning. Some sub-VFR conditions possible Wednesday into Thursday with maybe some showers around. VFR conditions expected later on Thursday and into Friday with high pressure building in && .MARINE... Winds will be light (at or below 10 kt) through Monday. Winds will generally be from the northeast, with some variation between north and east. Winds will increase Monday night and Tuesday as Maria nears. At this time Small Craft conditions possible in the mid Bay Tuesday, and expected Wednesday into Thursday with Hurricane Maria nearby. That could change contingent on the path/strength of Maria. Consult NHC products for updates. && .TIDES/COASTAL FLOODING... Water level excess has continued to ease through the day, now running between 2/3rds and 3/4ths of a foot above normal across much of the area. This draining has countered the astronomical gains, reducing confidence in any minor flooding tonight...even at St George Island, where an Advisory remains in effect. Am not making any additional changes at this time. These trends have been captured by the ensembles. If this guidance proves accurate-- which we will be monitoring for over the next couple of hours-- the Advisory may be cancelled. In light of these developments, we will be in monitor mode for early in the week. Its possible that tides will be peaking at the threshold between caution and minor flood for a couple of cycles. Eventually, water levels should be rising as Maria nears, but there is ample spread in the guidance by that point. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Coastal Flood Advisory until 10 AM EDT Monday for MDZ017. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...JE NEAR TERM...HTS SHORT TERM...HTS LONG TERM...IMR AVIATION...HTS/IMR MARINE...HTS/IMR TIDES/COASTAL FLOODING...HTS is the U.S. government's official web portal to all federal, state and local government web resources and services.