Area Forecast Discussion
Issued by NWS Sterling, VA

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775 FXUS61 KLWX 211447 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 947 AM EST Sat Jan 21 2017 .SYNOPSIS... A front will remain stalled over the region through today. Low pressure will impact the area Sunday through Monday before moving away Tuesday. A cold front will pass through the area Wednesday into Wednesday night and an upper-level trough may build overhead late next week. && .NEAR TERM /THROUGH TONIGHT/... Low clouds...areas of dense fog and drizzle will continue this morning for much of the region. A dense fog advisory has been extended through 11 am this morning for areas west of the I-95 corridor. Visibile satellite shows higher elevations such as ridges in sunshine this morning. Little change in the surface analysis is expected today and therefore fog and low clouds are going to slowly dissipate. Areas west of the Blue Ridge will likely dissapate quicker with patchy fog and low clouds persisting aganist the eastern slopes of the Blue Ridge through the early afternoon. Prev discussion... A warm front will stall out over the are today. The boundary is most likely to stall out across the northern Shenandoah Valley into the Virginia Piedmont. For locations north and east of the boundary...low clouds will likely hang around throughout the day...but dense fog and drizzle should dissipate later this morning. For locations south and west of the boundary...there will be some breaks of sunshine and it will be unusually mild for this time of year. Max temps are forecast to be in the lower to middle 50s across Maryland as well as the Washington and Baltimore Metropolitan areas...extreme northern Virginia and the eastern Panhandle of West Virginia. Went a few degrees below guidance due to the anticipated cloud cover. However...max temps are forecast to be in the lower to middle 60s in the central Shenandoah Valley where more breaks of sunshine are expected. The boundary will remain nearly stationary tonight and an upper- level disturbance will pass through the area during this time. A period of light rain is possible as the upper-level disturbance passes through. The best chance for rain will be from central Virginia into southern Maryland...but rainfall amounts will be light. More low clouds and areas of fog and drizzle are expected to develop tonight due to plenty of moisture trapped underneath the nocturnal inversion. Locally dense fog is possible. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... Cutoff low pressure in the southern stream of the jet will track through the Gulf Coast States Sunday before tracking northeast into our area Sunday night through Monday. An easterly flow will increase ahead of the low on Sunday and this will allow for moisture to move in from the Atlantic Ocean. At the same time...warm and moist air from the Gulf of Mexico will overrun the surface cooler air in place. The overrunning will allow for plenty of clouds along with period of rain. The best chance for rain will be during the afternoon. More rain is expected Sunday night. A soaking rain is possible as the low-level jet increases ahead of the approaching low. As the low tracks overhead Monday...the dry slot associated with this system will move overhead. Details and timing of the dry slot are uncertain at this time...but this may allow for a lull in the precipitation. As of now...it looks like a soaking rain is possible across all areas Monday morning...but rain may taper off across southern and eastern areas Monday afternoon. The surface low will begin to move away from the area Monday night...but the upper-level low associated with this system will remain overhead. More unsettled conditions are likely. Rainfall amount Sunday through Monday night are forecast to be around 1-2"...but confidence is low due to the uncertainty with the potential dry slot on Monday. Should the dry slot move in quicker...which some of the latest guidance is suggesting...then rainfall amounts will be less. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Primary area of wraparound precipitation from low pressure system will be tapering off by Tuesday morning...with at most a few lingering light showers from DC northeastward. Breezy W/NW winds and relatively warm conditions will remain Tuesday as heights rise over the area. Remaining dry Wednesday as high pressure slowly weakens over the area in advance of next system. Cold front poised to cross the area Wednesday into Thursday. Best forcing for ascent passes by to our north...while better moisture resides across the Carolinas...leaving us in between. Thus, precipitation chances will be rather minimal for our area (except along the Allegheny Front where upslope precipitation is expected)...with only light amounts anticipated. Main impact will be a drop in temperatures back closer to seasonable averages by Friday. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... Low clouds and areas of dense fog will continue through late- morning. Sub-IFR conditions are expected during this time. Vsbys and cigs may improve a bit this afternoon...but IFR conditions are still expected. There is a chance that MVFR cigs could develop for a brief period later this afternoon. Clouds will lower again tonight into Sunday morning and areas of dense fog and drizzle are expected. There may even be a period of steadier light rain as an upper-level disturbance moves through. SubIFR conditions are forecasted during this time. Steadier rain may develop later Sunday into Monday. IFR conditions are possible during this time as the cloud deck remains low. A dry slot may improve conditions a bit for later Monday into Monday night...but more showers are possible. Becoming mostly VFR Tuesday morning as low pressure system moves away...with only a few lingering light showers remaining. Though, breezy conditions will continue through Tuesday...before subsiding Tuesday night. VFR Wednesday with dry weather...as high pressure briefly nudges into the area. && .MARINE... An onshore flow will continue through tonight...but wind speeds should remain light. Low pressure will track through the Gulf Coast States Sunday. An easterly flow will strengthen during this time. A Small Craft Advisory is in effect for the Bay and lower Tidal Potomac River Sunday afternoon. Low pressure will approach the waters from the south and west Sunday night before moving overhead Monday. The pressure gradient will continue to strengthen ahead of the low. A Small Craft Advisory will be needed for the waters Sunday night into Monday and a Gale Warning may be needed for portions of the waters during this time. Gusty NW winds exceeding SCA criteria remain Tuesday behind departing low pressure system. Winds slacken late Tuesday as influence from low wanes. Mostly dry cold front crosses the waters late Wednesday into Thursday...with gusty winds possibly to SCA criteria behind it Thursday afternoon. && .TIDES/COASTAL FLOODING... An onshore flow will continue through tonight...but it should be light. Therefore...elevated water levels are expected but tidal flooding is not expected. An easterly flow will strengthen Sunday into Monday. This may cause anomalies to increase during this time. Minor tidal flooding is possible near night tide...especially late Sunday through Monday. An offshore flow will develop behind the departing low Monday night into Tuesday. Minor flooding is still possible Monday night since exact timing of the offshore flow is still uncertain as of now. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Dense Fog Advisory until 11 AM EST this morning for MDZ003>006- 502-503-505-507. VA...Dense Fog Advisory until 11 AM EST this morning for VAZ025>031- 036>040-050-051-501-504-505. WV...Dense Fog Advisory until 11 AM EST this morning for WVZ050>053- 055-502-504-506. MARINE...Small Craft Advisory from noon to 6 PM EST Sunday for ANZ530>534-537>543. && $$ SYNOPSIS...MSE NEAR TERM...BJL SHORT TERM...BJL/HSK LONG TERM...MSE AVIATION...BJL/MSE MARINE...BJL/MSE TIDES/COASTAL FLOODING...LWX

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