Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 300859 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 359 AM EST Wed Nov 30 2016 .SYNOPSIS... Low pressure over the upper Great Lakes will track into eastern Canada tonight. An associated cold front night will push through the Mid Atlantic late tonight. High pressure will return to the region Friday and Saturday. Low pressure will track to the west of the region Sunday night. High pressure returns Monday. && .NEAR TERM /TODAY/... As of 3 am, persistent vertically stacked/occluded low with 997mb surface low centered over the Twin Cities of MN. Longwave trough axis is ejecting onto the southern Great Plains. Weak surface flow and moisture from rain yesterday caused areas of dense radiation fog to develop. Dense Fog Advisory is in effect until 7 am for most of the CWA (Srn MD and Potomac Highlands are exception). Thick clouds are spreading NE across the and have reached the Blue Ridge. There are fewer 1/4SM reports west of the Blue Ridge now, but will need to keep the advisory at least for now. NErn sections of the CWA stand the best chance to have an extension to the fog advisory. Showers and isolated thunderstorms area spreading north from SWrn VA. RAP has some MUCAPE where current lightning is, but not in the SWrn section of the LWX CWA, so only rain/showers will continue to be forecast for the morning. Instability is expected to develop SE of the main slug of rainfall by midday with negative LI`s at 18Z according to the 00Z GFS. A marginal risk is in effect across the area with the strong low level jet potentially mixing down with the strongest activity. Furthermore, discrete super cells are possible east of I-95 (most likely for southern MD). Hence a 2 percent tornado risk. Expect locally heavy rain with QPF generally half inch with locally one or more inches. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... The longwave trough axis currently over the southern Great Plains will reach the mid-Atlantic by sunrise Thursday. An associated cold front will cross the area tonight, clearing out rain. Gusty west wind up to 30 mph both Thursday and Friday with little upslope snow. Maxima mid to upper 50s in dry air advection Thursday and five or so degrees less Friday after continued cold air advection.. && .LONG TERM /SATURDAY THROUGH TUESDAY/... High pressure will reside over the east coast Saturday. With the upper level flow in a zonal pattern temperatures will be right around climo norms for the beginning of Dec - near 50. Radiational cooling will allow temps to fall to around or slightly below the freezing Saturday night. Last night the models had some differences regarding the Sunday forecast but these seem in better line today. An open short wave is expected to track to our NW while high pressure moves into the Atlantic. There`ll be a chance of rain during the afternoon in the central Shenandoah Valley..with the moisture tracking north Sunday night. We are presently forecasting mixed precipitation west of I-95...but confidence is low with regard to the frozen precip. The high moving away means that cold air will not be held to our north which is essential..especially in a marginal situation like this. Lows expected to be in the lower to mid 30s. High pressure returns for Monday. Highs near 50. Monday night lows in the lower 30s. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... Areas of dense fog with LIFR cigs across the central Mid-Atlantic early this morning will slowly lift/diminish as clouds and rain spread northeast across the area through sunrise. However, IFR conds expected to prevail into the afternoon as potentially gusty showers cross the area continues. Isolated thunder risk this afternoon and evening, particularly southeast of DC. South winds increase by midday with gusts into the 20 kt range. Cold front crosses the area after midnight tonight with a shift to west winds. Gusts in 25 kt range Friday and Saturday with VFR conds. VFR conditions Saturday into the at least the first part of Sunday. Clouds are expected to increase Sunday night with a chance for precipitation. && .MARINE... Just like yesterday, south winds increase today as rain overspreads the area through the morning. Gusty showers and isolated thunderstorms may trigger special marine warnings, particularly in the afternoon. A cold front crosses the area tonight with a shift to west winds after midnight. West winds mix down through Thursday with gusts around 25 knots across the waters. SCA through Thursday for now and is likely again both Friday and Saturday. SCA level wind gusts possible Saturday. No problems foreseen Sunday. && .COASTAL FLOOD... Southerly flow continues on the water today ahead of a cold front that will cross late tonight. Winds will generally be 15 knots gusting 20 knots which would not cause much of a surge and the forecast is for water levels to remain a few inches below minor flood thresholds for the preferred high tide this afternoon and evening. However, stronger winds may mix down as showers and isolated thunderstorms cross this afternoon. A stronger surge could occur with this activity, perhaps raising levels to minor coastal flood levels. New moon is today. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Dense Fog Advisory until 7 AM EST this morning for DCZ001. MD...Dense Fog Advisory until 7 AM EST this morning for MDZ003>006- 011-013-014-016-502>508. VA...Dense Fog Advisory until 7 AM EST this morning for VAZ025>031- 036>040-050>057-501>508. WV...Dense Fog Advisory until 7 AM EST this morning for WVZ050>053- 055-502-504>506. MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ530>532- 535-538>540. Small Craft Advisory until 6 PM EST Thursday for ANZ533-534- 536-537-541>543. && $$ PRODUCTS...BAJ/WOODY!

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