Area Forecast Discussion
Issued by NWS Sterling, VA

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347 FXUS61 KLWX 201333 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 933 AM EDT Wed Sep 20 2017 .SYNOPSIS... A ridge of high pressure will remain over the eastern United States through early next week. Hurricane Maria may approach the coast of the Carolinas by the middle of next week. && .NEAR TERM /THROUGH TONIGHT/...
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Upper-level ridge axis remains overhead this morning while an upper-level disturbance approaches from the west. A deformation zone overhead has allowed for mid-level clouds over the metro areas this morning. A few sprinkles cannot be ruled out...but clouds are expected to dissipate across these areas this afternoon as deformation zone weakens. A few popup showers are possible this afternoon into this evening across the Potomac Highlands into the central Shenandoah Valley as the upper-level disturbance approaches from the west. However...instability will be limited and forcing with this system is quite weak. Therefore...much of the time should turn out dry. Elsewhere...partly to mostly sunny skies are expected this afternoon and it will turn out quite warm with the upper- level ridge overhead. Max temps will be in the mid to upper 80s across most locations. High pressure both at the surface and aloft will build over the region as the upper-level disturbance shifts to the south tonight. Patchy fog will again be a concern. Lows will be mainly in the 60s.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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Northeast flow aloft will dominate Thursday through Friday night as ridge builds to our west and Jose stalls to the east. Jose should have little to no effect on our weather during this time, so it will be unseasonably warm and humid, but dry, with the ridging preventing any convection. Highs will be in the mid to upper 80s, with lows in the 60s. Patchy late night and early morning fog will be the main forecast concern, mainly in the more rural, inland locations.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/... Ridge of high pressure will gradually strengthen through early next week. Latest Euro is much stronger than GFS/GEFS with the h5 ridge showing a 591 decameter ridge. No wx is expected as a result. The first half of next week, flow will turn more onshore north of Hurricane Maria. Latest Euro has trended westward and slower with the track of Maria bringing it closer to the NC Outerbanks, but so far models have been inconsistent on track longitude thus far, limiting confidence. Please refer to NHC for the latest on Maria. && .AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
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VFR conditions are expected through this evening with high pressure in control. Patchy fog will be a concern again over the next several late night and early morning periods thanks to persistent high pressure and light winds. Best odds same as early this morning as described above. Other than that, should be VFR thru Friday night. VFR conditions through Sun with no sig wx.
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&& .MARINE...
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Will continue with the SCA for the middle portion of the Bay and lower Tidal Potomac River through late this morning...but it will be marginal. Jose will move away from the area this afternoon. Gusts will be close to SCA criteria...but the forecast has them capped around 15 knots for now due to a weakening gradient. From tonight through Friday night, high pressure and light winds will dominate, with no SCA concerns at present. Light winds through the weekend. Winds will start strengthening during the first half of next week as pressure gradient tightens in response to approaching Hurricane Maria.
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&& .TIDES/COASTAL FLOODING...
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Water piled up near the mouth of the Bay from Jose over the past couple days. Those anomalies have spread across the Bay and Tidal Potomac River. Anomalies over 1 foot above normal remain across the entire Bay...so elevated water levels are likely to continue for at least the next couple tide cycles through tonight...despite an offshore flow. Coastal Flood Advisories are in effect from Annapolis southward and across the upper Tidal Potomac River. A Coastal Flood Warning is in effect for St Marys County where moderate flooding is expected. Guidance continues to show elevated water levels for Thursday as well.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory until 11 AM EDT this morning for DCZ001. MD...Coastal Flood Advisory until 6 PM EDT this evening for MDZ018. Coastal Flood Advisory until 10 PM EDT this evening for MDZ014. Coastal Flood Warning until 7 PM EDT this evening for MDZ017. VA...Coastal Flood Advisory until 11 AM EDT this morning for VAZ054. WV...None. MARINE...Small Craft Advisory until noon EDT today for ANZ533-534-537- 541-543.
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&& $$ SYNOPSIS...LFR NEAR TERM...BJL/RCM SHORT TERM...RCM LONG TERM...LFR AVIATION...BJL/RCM/LFR MARINE...BJL/RCM/LFR TIDES/COASTAL FLOODING...BJL

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