Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 171432 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 932 AM EST Fri Feb 17 2017 .SYNOPSIS... High pressure will slide offshore of the southeastern United States coastline through today. A weak system passes nearby Saturday night into Sunday morning. A backdoor cold front will be near the region on Monday followed by the return of high pressure. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A warm front located over the Ohio Valley this morning will move northeastward towards the region over the rest of the day, crossing into the area during the afternoon, and be near the DC metro by the evening hours. This will lead to a temperature gradient across the Mid Atlantic today with highs in the 40s across northeast Maryland, near 50F in the DC Metro, and near 60F across central Virginia. Otherwise, we`ll be looking at a mix of sun and clouds today. Solid overcast deck of mid level clouds will dissipate over the remainder of the morning hours giving way to sunshine along with some high clouds. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... Warmup continues Saturday...with highs nearly 20 F above normal. M/U60s in most places...except right along the Chesapeake and Tidal Potomac where U50s/L60s will be more common. While we start the day sunny, clouds increase during the afternoon as a weakening disturbance approaches. This disturbance will bring a chance for some light precipitation to the area Saturday night into early Sunday morning (mainly south of Washington DC). Any precipitation expected to clear the area near daybreak Sunday leaving the rest of the day dry with increasing sunshine. Highs again well above normal (in the M/U60s). && .LONG TERM /MONDAY THROUGH THURSDAY/... A sharp ridge of high pressure over the area Monday will lead to warm, tranquil conditions. While the same ridge will be the influencing feature Tuesday, the result may be a little bit different. Current guidance suggests that the ridge axis will be atop the area, resulting in onshore flow. Hence, the forecast will have more clouds and cooler temperatures. The timing and strength of this will need to be watched. Potentially, this could result in a marine airmass advecting inland which would result in a much different forecast than previously advertised. Points east of the Blue Ridge would be most vulnerable. By Tuesday night, northern stream shortwave energy will be flattening the flow aloft (both mid and upper levels...850 mb and above). Heights looking a bit flatter than yesterday, which is allowing both GFS and especially the ECMWF to bring a surface front and associated precipitation east of the Appalachians Tuesday night into Wednesday. Any precipitation would be light (a few hundredths inch of rain). And, thermal profiles warm enough for this to be definitively rain. The subsequent front would be left behind across the area on Thursday. It remains to be seen how strong it would actually be. Consequently, forecasts will have mid range clouds and low end (20%) PoPs. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... VFR conditions expected to prevail through Saturday as high pressure remains in control of the weather. Weak disturbance moves through the area Saturday night into Sunday morning...with a chance for light showers. Light rainfall rates should keep flight restrictions rather marginal/brief...with perhaps a brief period of sub-VFR (best chance at KCHO). VFR returns after daybreak Sunday. VFR conditions should continue into Monday. Tuesday could be a little questionable, as there is a hint of onshore flow. What is yet to be determined is whether that would bring flight restrictions inland due to low clouds/fog. && .MARINE... Relatively light winds expected through Sunday...with the typical increases/decreases during the day/night due to diurnal mixing trends. Winds should primarily be 10 kt or less Monday and Tuesday. In terms of direction... northwest on Monday, but becoming onshore Tuesday as a ridge axis passes overhead. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...MSE NEAR TERM...MM/MSE SHORT TERM...MSE LONG TERM...HTS AVIATION...MM/MSE/HTS MARINE...MM/MSE/HTS is the U.S. government's official web portal to all federal, state and local government web resources and services.