Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
134 FXUS61 KLWX 200107 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 907 PM EDT Thu Sep 19 2024 .SYNOPSIS... Low pressure will continue to drift off the Mid-Atlantic coast through Friday with strengthening high pressure building north of the region. A weak backdoor front may impact the area Saturday into Sunday bringing an additional round of showers and thunderstorms. A strong front and area of low pressure over the Great Lakes and Upper Midwest look to push into the area by the early and middle part of next week. Temperatures will remain at or slightly above normal through Sunday. && .NEAR TERM /THROUGH FRIDAY/... Rain showers have ended across the region. Clouds are slowly dissipating across the region with additional clearing expected overnight especially in areas along and west of US-15. Patchy fog will be possible in some of the rural valleys. Lows will range from the mid 50s to mid 60s. The dry trend continues for Friday as low pressure pushes further offshore. An isolated shower or thunderstorm cannot be ruled out along the Blue ridge and back across the WV/VA Highlands given added instability and weak convergence. Highs will reach the lower to mid 80s for most areas. Friday night`s lows will fall into the mid 50s to mid 60s again, with patchy valley fog possible. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... There is better agreement amongst the guidance in regards to a backdoor cold front which looks to pass through the region late Saturday into Sunday. Upper level low pressure will continue to push further off the New England coast Saturday allowing for a slightly flatter upper level flow pattern overhead. Meanwhile, strong Canadian high pressure will remain blocked to the north as a result ultimately slowing the timing of the backdoor cold front into late Saturday afternoon and Saturday night. The boundary appears to be fairly weak with shortwave energy diving down through northwest flow. This will promote scattered shower and thunderstorm development especially in areas along and west of of I-95. The 12Z ECMWF, GEM, and GFS all show this in some fashion during the 18z/2pm Saturday-06z/2am Sunday timeframe. Capped PoPs at 30-40 percent (highest along the Appalachians) for now until there is better agreement from the ensemble data. Highs Saturday should now remain in the lower 80s while lows remain close to a persistence forecast. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Ridging will build over the region during the early part of next week, sliding offshore by Tuesday. A shortwave-trough will move across the eastern Great Lakes and northern mid-ATLC Tuesday flattening the ridge and increasing the risk of showers. During the second half of next week, a deep upper low drops into the area from the western Great Lakes and Midwest bringing cooler and more unsettled weather conditions. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/... Patchy MVFR to IFR fog remains possible at KMRB/KCHO late tonight into early Friday morning. High pressure will maintain VFR conditions Friday, with patchy fog possible Friday night at KMRB and KCHO. A backdoor cold front and shortwave disturbance may bring some showers and thunderstorms late Saturday afternoon and evening. Confidence in this has increased amongst the latest deterministic guidance although the confidence in coverage and intensity still remains low. No significant weather is expected to impact aviation Sunday into Monday. Northeasterly winds on Saturday shift to easterly Sunday afternoon, gusting 5 to 10 knots each day. Winds increase slightly on Sunday in the eastern portions of the forecast area with KIAD, KDCA, KBWI, and KMTN gusting 10 to 15 knots in the afternoon. Sub- VFR conditions return beyond this point as another front pushes in to the region. && .MARINE... Upper level low pressure will remain off the coast through the weekend as high pressure builds north of the region. Light northerly winds turn toward the east and northeast Friday into Saturday. A backdoor cold front looks to cross the waters Saturday afternoon into early Sunday morning bringing the renewed potential for a brief period of Small Craft Advisory conditions. Some marginal gusts up to 20 kts can`t be totally ruled out mainly over the middle and open waters of the bay Saturday evening into Saturday night. SCA conditions are possible Sunday afternoon into Monday. Winds northeast 10 to 15 knots gusts up to 20 kts late Sunday into Sunday evening, mainly over the main stem Chesapeake and Tidal Potomac. Winds becoming east then southeast 10 knots late Sunday night into Monday and Monday night. && .TIDES/COASTAL FLOODING... Anomalies remain highest along the tidal Potomac River and lower bay this afternoon. Several advisories remain in effect through this evening`s high tide. After remaining stable through tonight, water levels are forecast to rise into the weekend as offshore low pressure traps water in the Chesapeake. Combined with high astronomical tide levels, additional, and more widespread, coastal flooding can be expected. Some guidance suggests Annapolis and DC SW Waterfront could even approach moderate flood levels. Coastal flood issues look to persist into next week.A Coastal FLood Watch is in effect for Annapolis and the Anne Arundel County Shoreline late Saturday evening through Saturday night. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 2 AM EDT Sunday for DCZ001. MD...Coastal Flood Advisory until 6 PM EDT Saturday for MDZ014. Coastal Flood Watch from Saturday evening through late Saturday night for MDZ014. Coastal Flood Advisory until 8 AM EDT Sunday for MDZ016. Coastal Flood Advisory until 11 AM EDT Sunday for MDZ017-018. VA...Coastal Flood Advisory until 2 AM EDT Sunday for VAZ054. Coastal Flood Advisory until 8 AM EDT Sunday for VAZ057. WV...None. MARINE...None. && $$ SYNOPSIS...EST NEAR TERM...CPB/EST SHORT TERM...ADS/EST LONG TERM...LFR AVIATION...LFR/EST MARINE...LFR/EST TIDES/COASTAL FLOODING...LWX