165 FXUS02 KWBC 120704 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 304 AM EDT Sat Sep 12 2026 Valid 12Z Mon Sep 14 2026 - 12Z Fri Sep 18 2026 ...Hazardous heat continues over the Southern Plains as heavy rain and severe weather threaten the Middle/Upper Mississippi Valley and Upper Great Lakes early next week... ...Overview... An upper-level ridge will retrograde from the Southeast into the Central U.S. next week. This ridge will initially generate hazardous heat in the Southern Plains before reinvigorating monsoon storms capable of producing flash flooding over parts of the Southwest mid-to-late week. 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 Upper Great Lakes early-to-mid week. ...Guidance/Predictability Assessment... Models are generally in good agreement on the evolution of the Southern ridge, while uncertainty continues to plague the West Coast pattern. Some models signal an elongated trough swinging through the West and Central U.S. next week, whereas another camp of models suggest a split flow with energy detaching from the parent low, which swings across the northern tier, and sits over the Northwest late next week. A blend consisting of the deterministic GFS/ECMWF and their respective Ai models was utilized on day 3 before replacing the GFS with the GEFS on day 4 due to better clustering around a split flow solution over the West being depicted by the favored blend. The ensemble means are gradually increased through the rest of the period due to the timing and amplitude uncertainties surrounding the Western U.S. trough evolution mid-to-late week. ...Weather/Hazards Highlights... A potent low pressure system will move through the northern tier beginning on Monday. Anomalous moisture associated with this system will generate a multi-day heavy rainfall threat, with an isolated to scattered flash flood threat possible from the Central Plains to the Upper Great Lakes on Tuesday and Wednesday in particular. Slight risks (at least 15% chance) of excessive rainfall are in effect for portions of the aforementioned areas. There's also the threat of severe weather from eastern Nebraska through Iowa and into southeastern Minnesota and southwestern Wisconsin, where a slight risk (level 2/5) of severe weather is in effect. 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 between Monday and Wednesday. Temperatures moderate beginning on Thursday. The return of the Central U.S. ridge should reinvigorate monsoonal storms across the Southwest beginning early next week. Moist southerly flow into the Southwest could produce isolated instances of flash flooding across portions of eastern Arizona through much of New Mexico. Burn scars, dry washes and slot canyons are especially sensitive to any heavy rainfall that occurs. Additionally, persistent easterly flow across the Florida Peninsula along with an embedded weak upper low/trough will increase rainfall chances across the southern half of the state, as well as, specifically the urban corridor of Southeast Florida. Kebede/Snell 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 $$