Area Forecast Discussion
Issued by NWS Sterling, VA

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402 FXUS61 KLWX 131520 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1020 AM EST Mon Nov 13 2017 .SYNOPSIS... A weak low pressure system will move east into the Atlantic Ocean today, followed by high pressure on Tuesday and Wednesday. Another front will cross the area Wednesday night into Thursday morning with high pressure moving back in for Friday. && .NEAR TERM /THROUGH TONIGHT/...
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Rain exited the area by 7AM today, but low clouds have stayed. Synthetic satellite imagery from the NSSL-WRF ARW shows lots of breaks developing in the clouds by 19Z or so with the only exception over the Appalachians and southern MD and the Chesapeake Bay. Warmer today with highs around 50F east of the Blue Ridge. Tonight, high pressure will slowly build in from the west. We will have some lingering clouds and low level moisture along with a light northerly breeze. This may be enough to keep fog from forming, as suggested by stat guidance, but model soundings suggest fog is possible. For now have not put in forecast just yet, but definitely a concern if we can clear enough and the winds can drop off enough. Lows will be in the 30s.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... High pressure will slowly cross the area Tuesday and Wednesday before a front approaches Wednesday night. This high will be a bit dirty, with a lot of lingering low level moisture, so the potential for fog and low clouds is elevated - however, at this point we have not explicitly included it in the forecast. It is just something to watch for. Otherwise, temperatures should be closer to normal, but not quite back to normal, with highs reaching the low 50s in the warmer spots and higher 40s in the cooler spots, with lows in the 30s overall. Cold front moves into the region Wednesday night, with a few showers. Timing for showers right now looks best west of I-95 before midnight, and then a bit later east of I-95. However, forcing is weakening as it moves through, so most likely showers will be weakening as well as they push across the CWA. Lows will be a little milder, but still a lot of 30s and 40s. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A surface cold front will depart east of the area Thursday morning. Clouds and a stray shower will be possible along the Mason-Dixon line with upslope showers likely through Thursday afternoon as the upper trough axis pivots across. Ridging at the surface and aloft will quickly pivot across the eastern U.S. on Friday. Meanwhile, a large/deep trough will dig towards the Great Lakes. This trough will induce strong surface cyclogenesis over the eastern Great Lakes by Saturday, dragging a strong cold front across the Mid-Atlantic. Showers and breezy conditions are likely during this time, but precipitation should be all liquid as we will be solidly in the warm sector. Surface low pressure occludes. This surface feature and the parent upper low (which becomes cut off by this time) will stall or move slowly across the Northeast Sunday into Monday. This will leave the Mid-Atlantic in a cold and blustery northwest flow. Below to well below normal temperatures are strongly favored during this time. Upslope snow showers would seem likely as well given the pattern, and a few flakes could even jump east of the mountains given the strength/instability of the upper trough Sunday into Monday. && .AVIATION /15Z MONDAY THROUGH FRIDAY/...
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Cigs should gradually improve to VFR in the next couple of hours where it hasn`t so with lots of breaks developing by mid afternoon. Fog potential exists again Wednesday morning, but otherwise Tuesday and Wednesday should be VFR with light winds as high pressure passes on by. Cold front on Wednesday night could bring sub-VFR cigs/vis in showers. Mainly VFR Thu-Fri. N flow Thu 10-15 kts becoming light variable Thu night-Fri as high pressure builds in. Good model agreement leads to a high confidence forecast for this time range.
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&& .MARINE... Low pressure pulling east away from the region today should cause rain this morning to break for some sun later today. Winds look mostly sub SCA, but if there is just enough mixing, we could touch SCA criteria late today and tonight, or at times during the day Tuesday. Probability of sustained SCA looks low at this time so have not pulled trigger on one. Wednesday looks solidly sub-SCA as high pressure pushes across the area before a cold front arrives at night. SCA gusts likely Thursday into Thursday night in northerly channeling behind a cold front. Winds go light as high pressure builds in late Thursday night through Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...LFR SHORT TERM...RCM LONG TERM...DFH AVIATION...RCM/DFH MARINE...RCM/DFH is the U.S. government's official web portal to all federal, state and local government web resources and services.