Extended Forecast Discussion NWS Weather Prediction Center College Park MD 333 AM EDT Sat Sep 6 2025 Valid 12Z Tue Sep 09 2025 - 12Z Sat Sep 13 2025 ...Overview... An overall multi-streamed and amplified mean upper pattern over the lower 48 and vicinity for next week should prove slow to dislodge as broadly highlighted by a warming central U.S. ridge sandwiched between West Coast and East Coast troughs. In this pattern, wavy frontal systems will further focus rain chances from the Northwest/West to the Rockies/Plains with gradual flow translation. Heavy rain potential will especially persist across Florida and within a deeply moist axis channel up along/just off the coastal Southeast/Carolinas. This activity will remain on the leading edge of cooled Canadian airmass insurgence with multiple frontal surges down through the central and eastern U.S. next week. ...Guidance/Predictability Assessment... Recent GFS/ECMWF/UKMET and Canadian model solutions continue to be generally well clustered for early/mid next week and a favored composite blend is well supported by ensembles and machine learning guidance in a pattern with overall above normal predictability. For later next week, there is growing recent model uncertainty with energy and shortwaves feeding through the western U.S. mean trough and how that energy ejects downstream with time to the Rockies/Plains. The WPC forecast blend at these linger time frames instead favors less progressive/more amplified GEFS/ECMWF/Canadian ensemble means given pattern nature. The means also act to mitigate run to run model variances as consistent with individual system predictability. This approach maintains excellent continuity with the previous WPC forecast and is more in line with the latest 00 UTC model suite that trended significantly in this direction. ...Weather/Hazards Highlights... A wavy frontal system set to linger over Florida and up just off the Eastern Seaboard will provide a main focus for moisture to pool, leading to daily enhanced rainfall potential. Saturated grounds from pre-cursor rainfall warrant WPC Excessive Rainfall Outlook Marginal Risk area introduction for Tuesday into Wednesday from Florida to the coastal Carolinas. However, daily rainfall amounts from the coastal Southeast/Carolinas and up the coast offers uncertainty for how much convection occurs onshore/offshore on any given day. Small shifts in the wavy frontal boundary could produce significant differences in the rainfall amounts. The amplified/slowed pattern shift may allow more onshore nudging. An upper trough/low working through the eastern Pacific to the Northwest/West will produce multiple days of rainfall next week, expanding eastward with time from the Pacific Northwest/northern California into the northern Great Basin and Intermountain West. This cool season type of rainfall should be marked by moderate rates that are generally not enough to cause flooding concerns. The lowering heights aloft yielding cooler temperatures could produce snow for the highest elevations. Lead monsoonal flow should generally relax by next week for the West/Southwest, but lingering moisture/instability fueling showers are still possible. Activity may increase later next week as lower latitude moisture channels between the western trough and central U.S. ridge. Showers and storms could reach out from the Rockies to the Plains as consistent with a region with locally growing instability and boundary focus. 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 WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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