141 FXUS61 KLWX 310803 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 403 AM EDT Wed May 31 2017 .SYNOPSIS... A weak cold front will approach the region from the northwest today and then cross the region tonight. High pressure will dominate Thursday. Another cold front will approach from the north on Friday before stalling in the region Saturday. A wave of low pressure will move east along this stalled front Sunday into early next week. && .NEAR TERM /THROUGH TONIGHT/... Low clouds and fog abound again this morning with humid maritime air in generally the northeast quadrant of the area. Visibilities are gradually dropping across the area, and a dense fog advisory may ultimately be required. Showers and storms which continued to regenerate along a stationary front late last evening are ever so slowly weakening and exiting southern MD. On the opposite side of the CWA, showers associated with an upper impulse are crossing the Appalachians and may affect the northwestern part of the area before diminishing. While it may take well into the morning...and potentially midday in the Baltimore area...the low clouds and fog should eventually exit the area with the pressure pattern favoring a more SW flow. The slow exit of clouds may hold highs in the 70s near the Bay, but it should make 80 or better for much of the area. Surface troughing will develop in the lee of the mountains, which appears to be the impetus for afternoon thunderstorm development in addition to weak height falls. Upper jet on equatorward side of closed low in Ontario will mean plenty of shear remains in place. There is some model spread in the quality of instability, but 1000 J/kg is possible from the Blue Ridge to I-95. Notably most hi-res models are fairly scattered in convective initiation. Have thus held POPs in the 30-40% range. Gusty winds will be the main threat with inverted-V profiles and dry mid level air. Activity will slide eastward this evening and end around midnight. Surface cold front will be approaching from the northwest and enter the area after midnight. It may be accompanied by some showers, but probabilities are low that they make it past the mountains. While some patchy fog is possible before the front arrives, dry air advection is expected with fropa. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Most models have the cold front south of the area by Thursday, which should result in dry weather and seasonable temperatures. Surface high pressure will slide across the area Thursday night. Some changes for the Friday and Friday night period, which is trending drier. The warm frontal zone won't have much instability or moisture to work with on Friday as it lifts northward. Then the surface cold front will begin to drop southward Friday night. This will offer the best chance of showers, though still far from certain. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Guidance is in relatively better agreement regarding the long term. Cold front slides southward into the area by Saturday before stalling in the region. This will result in an increased risk of showers and thunderstorms. The front will remain stalled nearby on Sunday as a wave of low pressure pushes east from the northern Plains. As the front starts lifting back north as a warm front, the chance of showers and thunderstorms will continue if not increase Sunday. Monday, we may pop into the warm sector, but the chance of showers and t-storms will remain. The surface low appears to get caught by an upper low Tuesday, resulting in continued inclement weather. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... While cigs remain on MVFR/IFR threshold this morning, bigger issue may be fog, which will be locally dense. Conditions gradually improve through the morning, taking the longest in Baltimore. However, it's looking like a better bet than the past couple days that skies clear out during the afternoon. Then attention will turn to potential thunderstorm development, although coverage is expected to be scattered. Storms will contain a gusty wind threat, but diminish by evening. Cold front will push through tonight. Don't have confidence at this time to include any fog prior to fropa. VFR conditions expected Thursday through Friday with high pressure. A cold front may bring a few showers Friday night. Increasing risk of MVFR to IFR conditions as we head through the weekend due to showers and t-storms, thanks to a stalling front and approaching wave of low pressure. && .MARINE... Onshore flow will become S/SW by this afternoon. Dense fog possible through this morning. Winds should remain below SCA conditions through today, though some gusty thunderstorms may reach the waters late this afternoon and evening. A cold front will move through tonight with westerly winds Thursday. Gusts could approach SCA levels, but have forecast 15 kt for now. Sub- SCA conditions continue Friday as high pressure moves across the area. Winds generally sub SCA this weekend, but shower and thunderstorm risk will be present Saturday and continue, if not increase, Sunday. && .TIDES/COASTAL FLOODING... Water levels remain high and should continue to be above normal for the today due to the persistent onshore flow, though it appears at least a brief break is in sight. Coastal Flood Advisories currently in effect for the next high tide cycle at St. Mary's and Annapolis. Additional advisories are possible today given expectation of lingering (though weakening) onshore flow. This would most likely be for Washington DC. Since right now it is forecast to be borderline, will hold off on advisory a little while longer. Its possible the next cycle falls just short of advisory level. By Thursday, northwesterly flow as high pressure builds in should finally allow anomalies to drop enough to end the minor coastal flooding. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 5 AM EDT early this morning for DCZ001. MD...Coastal Flood Advisory until 3 PM EDT this afternoon for MDZ014. Coastal Flood Advisory until 11 PM EDT this evening for MDZ017. VA...Coastal Flood Advisory until 5 AM EDT early this morning for VAZ054. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM TIDES/COASTAL FLOODING...RCM