641 FXUS02 KWBC 050659 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Sat Sep 5 2026 Valid 12Z Tue Sep 08 2026 - 12Z Sat Sep 12 2026 ...Prolonged late-summer heat wave lingers for the central/ southern Plains to the Mid/Lower Mississippi Valley through much of next week... ...Overview... An upper low near Montana on Tuesday will round the top of a persistent southern tier ridge, tracking over the Canadian Prairies to James Bay by Wednesday. This system brings showers to parts of the Great Lakes to Northeast and Midwest ahead of it Tuesday- Thursday. Energy dropping down the West Coast mid-week may cut off from the main flow and meander off the West for much of the period, likely meaning less direct moisture influx from Hurricane Marie. This low eventually looks to get absorbed into another shortwave into the Northwest late week, with deeper troughing over much of the West by next weekend allowing for the southern ridge to finally break down somewhat. ...Guidance/Predictability Assessment... Guidance is fairly agreeable Days 4/5 with the low tracking from Idaho Monday to Manitoba Tuesday with improving consensus on timing from there with the latest guidance runs. There is still a fair amount of uncertainty out West, though with trends now for a more offshore low. But where this low sets up seems dependent on how quickly what will be post-tropical Marie gets absorbed. Eventually this energy should phase with additional shortwave into the Northwest late week, but will plenty of uncertainty again on the timing. GFS is faster with more troughing over the West by the end of the period than the more offshore ECMWF. GFS and UKMET are most aggressive with remnants of Marie moving towards the West Coast early in the week. The WPC forecast was based on a general non-UKMET consensus for the early period, increasing to 60 percent ensemble mean guidance with the ECMWF for late period. Overall maintains good continuity with the previous shift as well. ...Weather/Hazards Highlights... The long duration Heat Wave is expected to linger over Mid/Lower Mississippi Valley to southern Texas through much of next week though may wane in intensity by later in the week. Key Messages remain in effect with several forecast record highs forecast. Cooler than normal temperatures on tap for early next week under the low/trough from the northern tier into the Northeast, but with moderation by late week as some ridging builds back across the South. The upper low through southern Canada will bring Tuesday-Thursday light to locally moderate rainfall along the main cold front as it sinks through the Midwest and Northeast. Monsoonal moisture will continue for the Southwest and southern Rockies through the week. Tropical moisture from Marie looks to generally remain offshore from California, though uncertainty still remains with this plume. Precipitation chances may expand more across the Northwest by next weekend with increasing troughing over the region. Santorelli 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 $$