Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241043 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 643 AM EDT Mon Apr 24 2017 .SYNOPSIS... Low pressure over Georgia will gradually move northeastward, reaching the South Carolina coast this evening, the North Carolina coast Tuesday evening, and finally off the Mid- Atlantic Wednesday. A cold front will approach the region late Thursday or early Friday and remain nearby through the weekend. && .NEAR TERM /THROUGH TONIGHT/... Cutoff low pressure over the southeastern CONUS this morning will slowly drift northeast into the Carolinas this afternoon through tonight. High pressure remains over New England. A northeast flow between these systems will continue to usher in unusually cool conditions for this time of year. At the same time...warm and moist air rotating around the low will overrun the surface cooler air in place resulting in plenty of clouds along with periods of rain. The steadiest rain will be over the Potomac Highlands into central Virginia through early this afternoon...where forcing will be stronger closer to the cutoff low and overrunning will be deeper. Farther north across the Washington and Baltimore Metropolitan areas into northern Maryland and easter West Virginia...rain will be light and more intermittent as it fights dry air advection at the low-levels. the low tracks a bit farther north and east later today through tonight. Overrunning will deepen across all locations and rain is expected to become more widespread. Rainfall amounts across central Virginia into the Potomac Highlands will be around one- half to one inch today through tonight. Rainfall amounts around one-quarter to one-half inch are expected across most other locations. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Low pressure will remain nearly stationary Tuesday over the Carolinas before slowly moving off to the north and east Tuesday night through Wednesday. A soaking rain is expected across most locations Tuesday along with plenty of clouds. Tuesday will be a bit milder compared to Monday...due to more of an easterly flow instead of northeast but still well below climo. Max temps will hold in the 50s for most areas with lower to middle 60s across the Virginia Piedmont into southern Maryland. Rain will gradually diminish in coverage Tuesday night through midday Wednesday as the low weakens and slowly moves away. Wednesday will turn out milder as weak high pressure builds overhead. Clouds should give way to sunshine across the Potomac Highlands and central Shenandoah Valley. Elsewhere...some breaks of sunshine are possible later in the day but clouds will be stubborn to break since they will be trapped underneath a strong subsidence inversion. This will impact temperatures...and this leads to high uncertainty. Tweaked max temps down a few degrees across central and eastern portions of the CWA. If clouds hang on all day...then max temps will hold in the lower to middle 60s but if clouds break sooner then max temps will be well into the 70s. The low will track well off to our north and east Wednesday night and weak high pressure will build overhead. Areas of fog are possible due to saturated soils and light winds. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Cold front forecast to be draped from Michigan southward to Mississippi/Alabama by 12z Thursday...with blocking high over the Atlantic. Front will try to push into the area...but will likely stall out it struggles to make progress into the area due to the aforementioned blocking high. Front expected to remain nearby through the weekend...with a persistent flow of warm/moist air advecting into the region. This will allow for warm/humid conditions to develop...with dewpoints climbing into the M/U60s by the weekend and temperatures in the M/U80s. Increasing instability will promote thunderstorm activity...coverage initially appears to be isolated or widely scattered for the end of the capping inversion and weak forcing reside over the area. Juicy airmass remains through early next week...with diurnally- driven thunderstorms chances remaining until moisture is scoured out with next frontal passage. Continued moistening will lead to moderate/strong instability over the weekend...with strong storms possible. Front likely focus for will need monitor spatiotemporal forecast trends of front over the next several days. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Low pressure will track toward the Carolinas today and remain nearly stationary through Tuesday before slowly moving away from the area Tuesday night through Wednesday. Warm and moist air will overrun cooler air near the surface...resulting in low clouds along with periods of rain. Timing of the lower cigs remains uncertain because drier air is advecting in at the lower levels. For looks like best chance of MVFR through mid-morning will remain across KCHO with VFR elsewhere. Most guidance continues to hint at low-level drier air advecting into the area through most of this afternoon. Therefore...VFR conditions may persist for most of the terminals. Did allow for MVFR conditions for KCHO but even there confidence is low. Intermittent light rain is expected during this time. Overrunning will deepen late this afternoon through Tuesday and this will increase rainfall coverage and lower cigs to IFR levels. Low clouds will persist through at least Wednesday morning before possibly breaking up Wednesday afternoon. Areas of fog are possible Wednesday night due to saturated soils and light winds as high pressure builds overhead. VFR conditions Thursday. VFR should prevail Friday...though, isolated to widely scattered thunderstorms possible (especially during the afternoon/evening). && .MARINE... Low pressure will track across the southeastern CONUS this morning before becoming nearly stationary over the Carolinas this afternoon through Tuesday. The pressure gradient between the low and the high will strengthen during this time. A Small Craft Advisory is in effect for the waters. A Gale Warning may be needed for middle portions of the Maryland Chesapeake Bay and the lower Tidal Potomac River Tuesday. The strongest winds will be Tuesday morning through midday. The low will weaken Tuesday night and slowly move away from the area Wednesday. A Small Craft Advisory may need to be extended into Tuesday night for portions of the waters. Winds will remain below SCA criteria Wednesday through Wednesday night as weak high pressure builds overhead. Increasing southerly flow Thursday with wind gusts approaching SCA criteria. Winds decrease some Friday...though isolated to widely scattered thunderstorms possible (especially during the afternoon/evening). && .TIDES/COASTAL FLOODING... Easterly flow around low pressure to the south will foster persistent onshore flow over the waters through Tuesday...which will keep tidal anamolies elevated. Onshore flow will strengthen a bit today through Tuesday...with minor flooding possible near times of high tide. Though, it currently appears that all sites will remain below minor tidal flood stage for the next high tide cycle (still need to watch Straits). Better chance for minor tidal flooding this evening into Tuesday...especially at the most sensitive sites (Annapolis, Straits, and DC). The flow should gradually turn north Tuesday night into Wednesday as the low moves away from the area. Water levels should decrease during this time. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ530>543. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...MSE AVIATION...BJL/MSE MARINE...BJL/MSE TIDES/COASTAL FLOODING...MSE is the U.S. government's official web portal to all federal, state and local government web resources and services.