448 FXUS02 KWBC 050648 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 248 AM EDT Mon Oct 5 2026 Valid 12Z Thu Oct 08 2026 - 12Z Mon Oct 12 2026 ...Excessive rainfall/flash flood threat continues for Central Gulf Coast and Southeast through Friday... ...Heat wave in California begins to weaken on Thursday... ...Guidance/Predictability Assessment... Models continues to support a broad upper trough across eastern Canada into eastern U.S. while greatest spread develops over the western U.S. as the upstream eastern Pacific trough interacts with the western ridge. The latest guidance continues to differ on the timing and amplitude of the trough, especially towards the weekend. The forecast is based primarily on a multi-model/ensemble consensus, with increasing reliance on the ensemble means with time to mitigate deterministic run-to-run variability. This approach supported the large-scale agreement while smoothing some of the differences within individual shortwaves, frontal timing, and convective evolution.. ...Pattern Overview and Weather/Hazards Highlights... The broad mean trough over eastern U.S. will remain well established through the period, while a reinforcing shortwave rotating through the base will support another surface frontal progression across the Midwest, Great Lakes, and Northeast bringing cooler conditions behind the front. Farther south, the Gulf Coast/Southeast will remain comparatively warm beneath persistent southerly flow ahead of the slow-moving frontal boundary. Deep tropical moisture will continue to interact with the boundary, leading to showers and thunderstorm development across the Southeast, Gulf Coast, and Florida through Saturday. The combination of increasing low- level moisture, weak frontal progression, and locally favorable low- to mid-level flow may lead to excessive rainfall and localized flooding along the Gulf Coast. With the potential for repeated convection and high rainfall rates, WPC has placed a Marginal Risk across the Gulf Coast into eastern Texas coast and portions of western Texas in the Excessive Rainfall Outlook for Day4/Thursday. The Marginal Risk continues for the Gulf Coast into and western Texas for Day5/Friday. By Saturday, the heaviest rainfall axis starts to expand inland across the Southeast. On Sunday, a portion of the frontal boundary will gradually lift northward along the East Coast, spreading showers and thunderstorms from the Southeast into the Northeast. Across the West, upper ridging will continue to support dry and anomalously warm temperatures through Thursday. The strongest heat will persist for portions of California and Southwest, where highs are expected to reach 90s to low 100s. Warm overnight temperatures will also limit relief from the heat, leading to heat-related illness concerns especially for those without adequate cooling and hydration. The ridge will gradually weaken as the eastern Pacific approaches the coast by Friday. This will bring precipitation chances across the Pacific Northwest and northern Rockies, especially on Saturday into Sunday as the trough becomes more amplified. Showers will continue to expand eastward from the Pacific Northwest/northern Rockies into portions of the Midwest by Sunday, with locally moderate to heavy rainfall possible along favored terrain and frontal zones. Additionally, as the western ridge weakens, the trough will bring cooler temperatures that will spread across the Pacific Northwest into northern Plains through the weekend. Oudit 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 $$