Extended Forecast Discussion NWS Weather Prediction Center College Park MD 238 AM EDT Fri Sep 22 2023 Valid 12Z Mon Sep 25 2023 - 12Z Fri Sep 29 2023 ...Overview... The pattern features an upper trough moving into the West and a downstream Omega Block evolving into a Rex-like Block across the eastern portion of North America and the adjacent northwest Atlantic. ...Guidance Evaluation/Predictability Assessment... The guidance shows reasonably good agreement. For the 500 hPa heights, pressures, winds, and QPF, used a compromise of the deterministic 12z UKMET, 12z Canadian, 12z ECMWF, and 18z GFS early before utilizing increasing amounts of the 12z ECMWF/12z NAEFS ensemble means. The remainder of the grids were more heavily weighted on the 01z NBM. ...Weather/Hazards Highlights... An early season storm system will bring unsettled and active weather to the Pacific Northwest beginning late this weekend and through early next week. A few rounds of heavier precipitation are likely, favored for the coastal regions and upslope areas of the Washington and Oregon Cascades into northern California/southwest Oregon where some localized flooding may be possible with repeating rounds of moderate rainfall, particular in burn areas/burn scars near the western border of CA/OR Monday into early Tuesday. A fading front dropping into the southern Plains/western Gulf coast is expected to reinforce the polar front across the Gulf of Mexico as the parent upper trough slowly progresses from the Midwest into the Southeast and lead to the potential for heavy rainfall Monday into early Tuesday. Rainfall could be excessive in areas that have been wetter than average this past week and in around portions of south-central and southeast TX. The volume of rainfall near and east of the Appalachians mid to late next week remains a question mark as the guidance shows a variety of possible scenarios. Temperatures should be most above average across portions of the Plains/Midwest -- moreso on overnight lows -- and below average across portions of the Mid-Atlantic States and West, which will be most noticeable for daytime highs. Roth 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 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