Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
104 FXUS61 KLWX 091901 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 301 PM EDT Thu May 9 2024 .SYNOPSIS... Shower and thunderstorm chances continue through Friday as a slow moving front pushes south and east of the region. The front will bring the potential for severe weather and flooding to areas mainly south of Interstate 66 later today. Precipitation chances slowly decrease behind the front going into the weekend with cooler temperatures and high pressure nearing the area. Shower and thunderstorm chances along with warmer temperatures return by the middle of next week as high pressure pushes offshore. && .NEAR TERM /THROUGH TONIGHT/... A frontal boundary currently draped over the forecast area, will slowly push south throughout the afternoon before exiting the area this evening. North of the front, cool and stable air will limit severe thunderstorm potential, though heavy rain remains a threat. High temperatures north of the front will be in the 60s to low 70s with plenty of clouds expected. South of the frontal boundary, warmer temperatures and breaks in cloud cover will allow for increased instability and more favorable conditions for severe thunderstorm development. With CAPE 500-1000 J/kg and 50 knots of effective shear, isolated strong to severe thunderstorms are possible, mainly for those south of Cumberland to Washington DC. SPC has removed the slight risk from our area with the southwestern portion of the forecast area in a marginal risk for severe weather. While damaging wind gusts greater than 60 mph and large hail 1"+ remain the main threats, the tornado threat as diminished significantly. Storms will likely start developing in the next few hours, and will persist through the evening. South of the front, high temperatures will be in the 70s to low 80s. Thunderstorm chances diminish overnight as rain shower chances continue through Friday morning. As the frontal boundary drifts south of the forecast area, cloud cover will increase with overnight temperatures dropping into the upper 40s to 50s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... An upper level trough will pivot over the region Friday with a potent shortwave passing to our north. This will lead to continued shower and thunderstorm chances for the forecast area. In the wake of a cold front, temperatures will be noticeably cooler with high temperatures in the 50s and 60s for most. Those in the southernmost portions of the area will see high temperatures in the low to mid 70s where cloud cover will be less. Precipitation chances decrease gradually overnight Friday with low temperatures in the 40s to low 50. Saturday will begin dry with dry air aloft inhibiting any precipitation chances. A low pressure system approaching from the Great Lakes will bring increasing shower and thunderstorm chances Saturday afternoon. Temperatures will be in the 60s for most of the area. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Longwave troughing/upper level trough axis will swing offshore Sunday afternoon as mid and upper level ridging build back into the region. Some showers and isolated thunderstorms will be possible Sunday morning into Sunday afternoon especially north of I-66/US-50 where better forcing with the departing trough axis can be found. Areas further south will likely stay dry with surface high pressure building eastward from the Ohio River Valley into the central Appalachians region. Severe weather will not be concern although any showers or thunderstorms that due form could put down a brief downpour along with small hail. Monday looks to be our driest day of the next 7 days as 500 mb heights rise with surface high pressure sitting just to the south of the region. This will yield a nice late Spring day with highs in the mid to upper 70s underneath partly cloudy skies. Unfortunately, the dry time will be brief as an upper trough develops in the lee of the Rockies, and deepens as it tracks into the south central US and Gulf Coast states during the middle part of workweek. Meanwhile, high pressure will shift off the VA/NC coast Tuesday into Wednesday allowing for south to southeasterly return flow to ensue. This will allow Atlantic and eventually Gulf of Mexico moisture to increase across the region yielding daily isolated to scattered chances for showers and thunderstorms. Uncertainty remains in the placement and timing of the heaviest precipitation with a focus mid to late week (Wednesday and Thursday). This is due largely in part to a warm frontal boundary that will be lifting northward into the region. As for severe weather, it cannot be ruled out, but overall predictability remains too low at this point to pick a given day out. CSU learning machine and CIPS probabilities point toward the Wednesday and Thursday timeframe given the front lifting and added moisture lifting into the area. Highs will continue to be in the low to mid 70s for areas east of the Allegheny Front (60s). Lows will drop down mostly in the 60s during the middle part of the week. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... Conditions are currently VFR at all terminals with the exception of KMRB where IFR conditions are present. Conditions will drop to MVFR this evening and then IFR at all terminals tonight. Showers and thunderstorms could impact all terminals, bringing periods of reduced CIGs and VSBYs due to heavy rain. During thunderstorms, gusty winds are possible as well. The greatest chances for thunderstorms is at IAD, DCA, CHO, and MRB, but thunder cannot be ruled out at BWI and MTN. The best chances for showers and thunderstorms is this evening and into the overnight, with thunder chances decreasing right before midnight. IFR conditions continue Friday as precipitation chances linger. Conditions improve to VFR on Saturday. Winds shift to northeasterly tomorrow before becoming southerly on Saturday. SCA level winds return SUnday in the wake of a shortwave trough pushing offshore and high pressure building to the south. SCA conditions will likely continue Monday, Tuesday, and Wednesday as low pressure approaches from the south and high pressure pushes offshore. && .MARINE... Northeasterly to easterly winds will remain below SCA criteria throughout the day. Tonight, easterly winds may reach SCA criteria as a weak area of low pressure moves to the south of the waters. Winds diminish by early Friday morning. Winds remain out of the northeast on Friday, while blowing right at or just below SCA criteria in the afternoon. Rain showers and thunderstorms could impact the waters today and Friday, mainly in the afternoon. Winds shift to northerly Friday night before shifting to southerly for the weekend. SCA level winds return SUnday in the wake of a shortwave trough pushing offshore and high pressure building to the south. SCA conditions will likely continue Monday, Tuesday, and Wednesday as low pressure approaches from the south and high pressure pushes offshore. && .TIDES/COASTAL FLOODING... North to northeasterly winds should allow water levels to continue to decrease this afternoon and evening. Additional minor flooding is possible at some sensitive locations (Annapolis, Straits Point, and DC Waterfront) late tonight into early Friday morning as southwest flow returns. Levels should drop well off by Sunday when offshore northwest flow kicks in across the area. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...EST NEAR TERM...AVS SHORT TERM...AVS LONG TERM...EST AVIATION...AVS/EST MARINE...AVS/EST TIDES/COASTAL FLOODING...EST