160 FXUS02 KWBC 121944 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 344 PM EDT Sat Sep 12 2026 Valid 12Z Tue Sep 15 2026 - 12Z Sat Sep 19 2026 ...Hazardous heat lingers over the Southern Plains as heavy rain threatens the Middle/Upper Mississippi Valley and Southwest... ...Overview... An upper-level ridge/closed high will retrograde from the Southeast to the south-central U.S. next week. This ridge will support hazardous heat across the Southern Plains into later next week before finally moderating. Meanwhile, monsoon storms capable of producing flash flooding will reinvigorate over parts of the Southwest as moisture is channeled between the ridge and a western U.S. mean upper trough. Zonal to diffluent flow across the northern tier will support heavy rainfall and potentially severe weather across portions of the Middle/Upper Mississippi Valley and vicinity with frontal interction, but supporting shortwave timing/details remains uncertain in guidance. Western Atlantic upper/surface trough approach and passage across Florida into the northern Gulf also has potential to focus convection to monitor later next week. ...Guidance/Predictability Assessment... Medium-range guidance clustering has improved over the last few guidance cycles, but especially with the latest 06/12 UTC runs to bolster forecast confidence. A guidance blend with slightly more ensemble means/machine learning guidance emphasis later period seems to offer a consistent forecast basis for threat messaging. ...Weather/Hazards Highlights... A potent low pressure system will lift over southern Canada to Hudson Bay on Tuesday. The guidance signal has increased that anomalous moisture lifting into this system and pooling into a slowing trailing front will fuel a multi-day strong convective and heavy rainfall/flash flooding threat from the Central Plains and Mid-Mississipppi Valley to the Great Lakes Tuesday and Wednesday. Marginal and embedded Slight Risk threat areas are depicted on the WPC Excessive Rainfall Outlook (ERO) as linked below. A strong ridge (potentially a record max for mid-September per the NAEFS ESAT) over the South and Southeast will generate well above average temperatures across the Central/Southern Plains and into the Lower Mississippi Valley/Mid-South next week. Heat indices between 100-110 degrees may support major to locally Extreme HeatRisk over portions of the aforementioned areas into next midweek. Temperatures should moderate beginning on Thursday. The return of the Central U.S. ridge and emerging mean upper troughing into the West should provide a moisture conduit to reinvigorate monsoonal storms across the Southwest next week. Moist southerly flow into the Southwest could produce isolated instances of flash flooding from eastern Arizona through southeast Utah and New Mexico into the central Rockies. Burn scars, dry washes and slot canyons are especially sensitive to any heavy rainfall that occurs. The ERO maintains a Marginal Risk area. Additionally, moist onshore Atlantic flow over Florida along with southwestard passage of an upper low/trough will increase and maintain rainfall chances next week and subsequent emergence over the northern Gulf could support organized convection to monitor. 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 $$