909 FXUS02 KWBC 051752 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 PM EDT Fri Sep 5 2025 Valid 12Z Mon Sep 08 2025 - 12Z Fri Sep 12 2025 ...Overview... The flow pattern for next week should remain overall amplified and slow to dislodge with a Rockies to Plains ridge sandwiched between West Coast and East Coast troughs. In this pattern, wavy frontal systems will focus most rain chances over the Northwest/West and slowly out to the Rockies/Plains and also downstream over the Upper Midwest/Great Lakes with northern stream energy, from South Texas and the Gulf and especially across Florida, and an axis along/just off the coastal Southeast/Carolinas with moist southern stream flow. ...Guidance/Predictability Assessment... 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 in the week, there is a lot of uncertainty with energy and shortwaves through the larger Western U.S. trough, and how much energy ejects eastward into the northern Plains. Therefore, the WPC blend for the latter half of the week consists of a greater weighting towards the ensemble means to help smooth out the run to run variances. This approach maintains good continuity with the previous WPC forecast as well. ...Weather/Hazards Highlights... Monsoonal rainfall amounts should generally decrease by Monday, but some lingering moisture/instability fueling showers are still possible. Showers and storms could reach into much of the Plains to Upper Midwest consistent with a region of modest instability near another front. Not expecting this activity to be much of a concern for flash flooding at this time so no WPC Excessive Rainfall Outlook risk areas are depicted for Day 4/5 Monday/Tuesday, but central U.S. convection could continue as next week progresses to monitor. Farther east, the frontal system over Florida into the western Atlantic will provide a focus for moisture to pool, leading to at least scattered diurnal convection each day. Moisture levels look to decrease slightly over Florida compared to the short range period, but the saturated grounds from rainfall before Sunday warrant the addition of a Marginal Risk area for Monday from roughly Cape Canaveral to south Florida. Rainfall across the Carolinas into Georgia is rather uncertain with how much convection may occur onshore or offshore on any given day. Small shifts in the frontal boundary could produce significant differences in the rainfall amounts, but the amplified/slower pattern translation may allow for some onshore nudge. An upper low pushing through the eastern Pacific toward the Northwest 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. 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 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 $$