Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201418 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1018 AM EDT Tue Jun 20 2017 .SYNOPSIS... Weak high pressure will build over the area today and hold through Thursday. The next cold front will move across the area at the end of the week or early next week. && .NEAR TERM /THROUGH TONIGHT/... High pressure will be building into the area today. Air mass will be dry behind the cold front, and combined with subsidence we will be hard- pressed to generate diurnal clouds. Mixing will be rather deep: Model soundings suggest that momentum transfer will be supportive of some gusty winds; these have already been realized at MRB. Have increased wind forecasts through sunset. The remainder of the forecast on track. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... A shortwave-trough moving around base of upper level trough over the Great Lakes will swing through the area during peak heating on Wed. This may be enough to spark a few showers mainly across nrn and wrn zones along the Pennsylvania border and along the spine of the Appalachians. Have mainly slight to low chance PoPs over those areas. Any shra activity will dissipate quickly with sunset. Mid-level ridge then builds on Thu promoting a warming trend with temps likely to climb into the low 90s. Moisture from the Gulf and from potential Tropical Cyclone 3 will advect northward into the mid-Atlantic region Thu night into Fri. There are notable differences between global models on timing of moisture and thus showers reaching the area. Have slight to low chance PoPs across the southwest part of the fcst area. Moisture then gets entrained into a frontal system with risk of showers increasing for the end of the week. && .LONG TERM /FRIDAY THROUGH MONDAY/... The end of the week into the weekend is still shaping up to be an unsettled period as a frontal zone stalls out across the Mid- Atlantic. Temperatures through this period may depend some on clouds, precipitation, and frontal position, but overall should be near to slightly above normal. While the actual cold front will be north of the region Friday, a prefrontal trough will be located east of the Appalachians. At least some scattered showers and storms will be possible. Instability isn`t progged to be very strong, but shear profiles may increase with potential mid level jet streak. Some uncertainty exists for Saturday into Sunday in terms of the frontal position and what impact moisture (or even remnant low pressure) of the current disturbance in the Gulf of Mexico will have. Nevertheless, the environment will be characterized by high precipitable water and weak instability, so some periods of heavier rainfall are within the realm of possibility. A second cold front will drop south in response to a deepening upper trough over the Great Lakes, crossing the area sometime early next week. Behind it, below normal temperatures and low humidity will arrive. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... VFR conditions through Thu night. A slow moving cold front will result in the potential for showers and thunderstorms Friday into Saturday. && .MARINE... Winds have subsided below Small Craft Advisory criteria on the Bay for the time being. However, momentum transfer suggests some gusts will exceed Small Craft Advisory criteria this afternoon. Have raised the flag this afternoon...extending into the evening on the Bay and through the night for the mid Bay (Drum Point- Smith Point/Tangier Sound area). A cold front will approach from the northwest Friday and slip into the area on Saturday. At a minimum this will result in a better chance of thunderstorms. Southwest flow may approach SCA levels on Friday. Wind forecast becomes more uncertain into Saturday depending on strength of potential low pressure tracking along the front. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 9 PM EDT this evening for ANZ530>533-538>542. Small Craft Advisory until 6 AM EDT Wednesday for ANZ534-543. Small Craft Advisory until 6 PM EDT this evening for ANZ535>537. && $$ SYNOPSIS...LFR NEAR TERM...HTS SHORT TERM...LFR LONG TERM...ADS AVIATION...LFR/ADS MARINE...HTS/ADS

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