Extended Forecast Discussion NWS Weather Prediction Center College Park MD 425 PM EDT Thu Oct 12 2023 Valid 12Z Sun Oct 15 2023 - 12Z Thu Oct 19 2023 ...Guidance Evaluation/Predictability Assessment... There remains good agreement in the latest 00z/06z model guidance for Sunday and Monday allowing for a purely deterministic model blend as a starting point for the updated WPC forecast progs today. By Tuesday/Day 5, some detail differences begin to emerge as energy from an initial shortwave over the Midwest closes off into an upper low as it moves towards the Mid-Atlantic/Southeast. This affects placement of a surface low off the East Coast, and any potential rainfall impacts for coastal regions. Out West, timing of the next short wave into the coast becomes an issue as well and even more so late next week as the trough deepens over the central U.S.. The WPC forecast for today incorporated increasing amounts of the ensemble means by late in the period to mitigate these differences, with some contribution from deterministic solutions as well to allow for a little extra detail/system definition. This maintains good continuity with the overnight WPC forecast as well, with only insignificant changes needed for todays forecast. ...Weather/Hazards Highlights... A dynamic upper trough/closed low and deepened surface low/frontal system will track through the Mid-Atlantic this weekend, leading to reformation as a coastal low/storm and maritime threat by Sunday. Expect some enhanced winds and mostly light wrap-around precipitation to exit the East Coast after Sunday. Additional energy into the upper low over the Mid-Atlantic/Southeast may spawn additional cyclogenesis off the East Coast around Tuesday, though rainfall impacts for coastal locations remain highly dependent on proximity of the system to the coast and any possible interactions with associated inverted troughing across the Mid-Atlantic/Northeast. Meanwhile upstream, the next shortwave should reach the coast on Monday, bringing moderate to heavy precipitation for the Northwest, favoring southern facing terrain of the Pacific Northwest/Olympics. However, low enough precipitation rates do not seem to warrant an excessive rainfall risk area at this time. Moisture should work its way inland through the middle of next week, but generally remain light and non-hazardous. Precipitation chances may increase again across the Central U.S./Midwest too as the trough deepens over the Central U.S. next Wednesday/Thursday. The cold front sweeping across the eastern U.S. into Sunday will bring temperatures generally 10 to 15 degrees below normal, including as far as south Florida. Meanwhile, a building ridge over the west-central U.S. brings temperatures generally 5 to 10 degrees above normal west from the Rockies to the eastern lee of the Cascades, with brief moderation on Wednesday as shortwave energy works its way inland. Santorelli/Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Flooding possible across portions of the Northern Plains. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw