Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210801 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 401 AM EDT Mon Oct 21 2019 .SYNOPSIS... High pressure will briefly build over the region today as the remnants of Nestor head out to sea. A cold front will approach from the west tonight before crossing the region later Tuesday into Tuesday night. High pressure will build back across the region Wednesday. Another storm system may approach the region during the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of early this morning, Nestor`s remnant low pressure, still a potent extratropical system, is east of Ocean City MD and continuing to head out to sea. Low level moisture remains high, however, and low clouds are persistent. Those few areas which have seen the low clouds break have seen patchy fog develop, and this risk will continue until after the sun rises. Those areas which remain cloudy through sunrise should see the clouds gradually break as the morning progresses thanks to a weak ridge of high pressure building southward from southern Canada, so most locations should see more sun than clouds by mid afternoon. The sun will aid temp rises, and we should rebound well into the 60s across most of the region, with some places flirting with 70. Winds will be northerly this morning, becoming light and variable by afternoon as Nestor`s influence wanes. Tonight, most areas start out mostly clear, but the approaching system from the midwest will begin to spread high clouds across the region. The southeasterly flow which will develop ahead of the system will also aid low-level moisture advection, and low clouds are likely to develop too. There may even be some patchy fog in spots, though it is more likely to be mist or even a little drizzle later at night. A few showers might reach western zones by night`s end, but most areas likely stay relatively dry through tonight. With the southeasterly flow and increasing clouds, lows likely stay mild, with 50s common. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Cold front approaching from the west is the main player in the short term. Guidance depicts a neutral or even weakly positively tilted trough aloft with the best forcing staying north. At the surface, most models depict a wave forming along the front to the south, which may pass over southern MD as the system crosses the region, though it also might stay just south. The implication here is that while rain showers are very likely, and there is some shear present, the surface instability is not significant and upper-level forcing also is not particularly helpful. Thus, have POPs going categorical in the afternoon and evening from west to east across the CWA on Tuesday as the front crosses the region and the wave of low pressure moves on by, but have held back on any thunder mention thus far. Can`t rule it out completely, but odds look to low to include in main forecast at this point. Otherwise, the relatively late arrival of the front and mild start should allow most of the region to rebound into the 60s by afternoon, though likely it will stay a little cooler than today thanks to the clouds. Front sweeps through during the evening and cooler air moves on in, with the rain showers quickly ending. It will be breezy as well, but not particularly windy behind this one. High pressure will then dominate through the following 24 hours, but with the center staying well south, downslope flow and relatively mild air flowing over the top of the high should keep temps fairly benign, with 60s expected once again Wednesday. Some lows may reach the 30s Wednesday night in the colder locales, but think it won`t be quite as cold as Friday night was. With many of our colder zones now cleared from further frost/freeze headlines thanks to the widespread freeze on Friday night, do not currently anticipate widespread frost/freeze headlines for Wednesday night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Sprawling high pressure will build from the Tennessee Valley across the Mid-Atlantic Thursday into Friday with mainly dry weather anticipated, though a weak shortwave likely swings by to our north on Friday with a bit of an increase in clouds, especially near the Mason-Dixon line. High temperatures generally 65-70 expected late this week, which is right around normal for late October. Model timing discrepancies continue for the potential storm system next weekend, though have mostly backed off precip chances for Friday (except for GFS/GEFS). Have focused PoPs Saturday night into Sunday. Timing uncertainties stem from when an upper trough approaches from the west, which will depend on whether or not it remains attached to larger scale westerly flow (quicker progression, trending less likely) or cuts off (slower eastward progression, trending more likely). && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Low cigs in the MVFR range likely linger into the morning hours, and locations which see breaks (i.e., CHO) will then run the risk of IFR vsby with fog developing. Improvement looks likely by late morning with VFR by early afternoon at latest. However, southeasterly flow may bring low cigs back to the region later tonight which could persist most of Tuesday into Tuesday evening, accompanied by showers by Tuesday afternoon. VFR likely returns behind a cold front Tuesday night, which should persist under high pressure through Wednesday night. VFR expected in SW flow Thu-Fri. && .MARINE... SCA gradually winding down early this morning as Nestor`s remnants slowly head out to sea. Expect all headlines gone by noon if not sooner. Light winds likely tonight under high pressure, but SCA may develop just ahead of a cold front Tuesday afternoon. SCA then more likely behind the front Tuesday night into Wednesday before dropping off by Wednesday night. Gradient should remain light enough to preclude any SCA level winds Thursday into Friday as high pressure builds overhead. && .TIDES/COASTAL FLOODING... Water levels have decreased on northeast to north flow, but water remains piled (anomalies of +1.5) at the mouth of the Chesapeake Bay. This water will return northward through Tuesday as winds become southeasterly, which will likely result in widespread minor to perhaps near moderate flooding (most likely moderate flooding would be at Straits Point and Annapolis, slightly less likely but not out of the realm of possibility near DC/Baltimore). && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 9 AM EDT this morning for ANZ532- 533-539>542. Small Craft Advisory until noon EDT today for ANZ534-537-543. Small Craft Advisory until 6 AM EDT early this morning for ANZ531. && $$ SYNOPSIS...RCM/DHOF NEAR TERM...RCM SHORT TERM...RCM LONG TERM...DHOF AVIATION...RCM/DHOF MARINE...RCM/DHOF TIDES/COASTAL FLOODING...DHOF is the U.S. government's official web portal to all federal, state and local government web resources and services.