Area Forecast Discussion
Issued by NWS Sterling, VA

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548 FXUS61 KLWX 170057 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 857 PM EDT Sat Jul 16 2016 .SYNOPSIS... A weakening cold front will remain in the area through tonight. The front will dissipate Sunday. Another cold front will cross the area Monday night and Tuesday with high pressure building in for Wednesday through Friday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Earlier convection has diminished to showers SE of I-95. These will continue to exit the area over the next few hours. Additional thunderstorms have formed closer to the actual surface boundary in PA as shortwave energy approaches. Currently, the only shower targeting our forecast area is pushing east from Garrett County MD. Will leave low end POPs across the northern tier to account for this through midnight. Would think diurnal stabilization (in addition to that provided by earlier storms) would take care of these small showers, although some models try to produce convection overnight. Will keep forecast dry after 2 AM for now, but will monitor trends. There should be enough breaks in the clouds for radiational cooling to occur, and temperatures aren`t too far from the dewpoints due to the rain. Therefore some fog is expected, although extent is uncertain. Minimal changes needed for low temperature forecast...ranging from near 60 in the western areas to mid 70s in the urban centers. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... High pressure just barely nudges in from the north on Sunday as the frontal boundary dissipates. Heights will also rise. However...given lack of true cleansing of the atmosphere and expected continuation of hot weather...an isolated thunderstorm mainly south and east of I-95 can`t be completely ruled out...though put the odds at 10 percent. Thus...its not in the forecast right now. Winds shift southerly again Sunday night into Monday as next front approaches. There is considerable difference among the guidance about just when this front crosses the area...with the Canadian suite showing significant convection Monday afternoon/evening with frontal passage overnight...the EC with less convection and a early Tuesday frontal passage (these likely are related)...and the GFS also not showing much convection but showing a later Tuesday passage. Given that...it was hard to concentrate PoPs or go very high with them during this period...but certainly potential of showers and t-storms exists. Highs on Monday should spike a few degrees ahead of the front with mid-90s expected...though heat indices should stay below advisory levels. Cooler Tuesday. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... High pressure builds into the area Wednesday and lasts through at least Thursday. Wednesday likely the most pleasant day, with relatively low humidity and seasonable temperatures. While temperatures rise each day through the end of the work week, humidity stays relatively low...so not too uncomfortable. Return of southerly flow late in the week would help to gradually increase humidity by early next weekend. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... Convection has pushed east of the terminals. Some forecast models indicate isolated overnight showers, but I do not think this is a likely outcome. The bigger concern overnight will likely be fog due to moisture from rain and clearing skies...potentially affecting all terminals except DCA. Have kept MVFR vsby for now due to uncertainty. Dry conditions and VFR expected Sunday. Patchy fog possible in climatological locations Monday morning. Next chance of storms starts Monday afternoon through Tuesday with next front. Wednesday-Friday look VFR with high pressure. && .MARINE... Weakening showers continue to push across the Bay and lower tidal Potomac through mid-evening. Although lightning has waned, still seeing some scattered gusts from the outflow up to 30 kt. Have covered this with an MWS as upstream obs show winds quickly diminish as showers exit. Should be better conditions Sunday with weak high pressure. Northwest flow becomes southerly late. Southerly channeling with SCA conditions possible Sunday night into Monday night with t-storms also possible late Monday into Tuesday, all associated with next cold front. SCA with northwest flow behind front also possible later Tuesday. Likely to drop below SCA Wednesday thru Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...RCM LONG TERM...MSE AVIATION...ADS/MSE/RCM MARINE...ADS/RCM

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