342 FXUS02 KWBC 131855 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Sun Sep 13 2026 Valid 12Z Wed Sep 16 2026 - 12Z Sun Sep 20 2026 ...Hazardous Heat subsides over the South-Central U.S. mid-late week as heavy rain/strong thunderstorms threaten the Central Plains, Middle/Upper Mississippi Valley and Southwest... ...Overview... Upper ridging that has been supporting hazardous heat in the South will weaken later this week, leading to some moderation in temperatures across the Central and Southern U.S.. Flow between the ridge and digging trough energy over the West will meanwhile provide a moisture channel as a stream of mid-level vorticity lobes lift from Mexico. This will generate monsoon storms from the Southwest through the South-Central Rockies. Trough development over the West has improved guidance support to provide cooling and unsettled conditions, but limited precipitation. Persistent diffluence and frontal system moisture/instability pooling will support a multi-day threat for heavy rainfall/flash flooding for the Central Plains and Middle/Upper Mississippi Valley. Frontal system progression should also spread chances for showers and thunderstorms into the Eastern U.S. late week into next weekend. There is also a consistent guidance signal to bring a compact Atlantic closed upper low/trough southwestward over Florida Thursday and then slowly westward across the northern Gulf Friday/next weekend. This feature may act to organize Gulf convection and associated marine and coastal threats to monitor. ...Guidance/Predictability Assessment... Guidance clustering has improved to bolster forecast confidence, but some flow embedded system timing differences remain. Favor a multi-model and ensemble mean/machine learning guidance composite to mitigate variance as consistent with individual predictability. This provides a consistent forecast basis for threat messaging. ...Weather/Hazards Highlights... A quasi-stationary front/baroclinic zone draped across the Central Plains and Middle/Upper Mississippi Valley will act as a focus for anomalous moisture to generate a multi-day heavy rainfall event beginning on Tuesday. Scattered to isolated thunderstorms are also anticipated along the front. The axis of heaviest rainfall is likely to occur between eastern Kansas/Nebraska into northern and western Illinois, where WPC Excessive Rainfall Outlook (ERO) Slight risk areas are in effect Tuesday-Thursday. The threat may then lift to the Upper Midwest/Great Lakes Friday/Saturday to monitor. Meanwhile, lobes of shortwave vorticity streaming north out of Mexico should interact with anomalous moisture and modest instability to generate monsoon storms across the Southwest this week. ERO Slight risks areas are in place from eastern Arizona to New Mexico through this Thursday. Slot canyons and dry washes are especially susceptible to flash flooding from any storms that develop. On Wednesday, heat indices between 100-110 along with lows in the mid-to-upper 70s will produce widespread major to extreme heat risk across the Southern Plains and Lower Mississippi Valley. A weakening ridge will support moderating temperatures later week. Kebede/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, 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 $$