Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Wed Sep 02 2020 Valid 12Z Sat Sep 05 2020 - 12Z Wed Sep 09 2020 ...High heat for parts of the Western/N-Central U.S. this week turns much colder early next week... ...Weather/Hazard Highlights and Guidance/Predictability Assessment... As per an amplifying upper level pattern expected to evolve over the course of the medium range period over the CONUS, temperature anomalies remain one of the main sensible weather headlines. The amplified pattern will open up the northern portions of the country for periodic intrusions to Canadian high pressure, the first of which is expected to arrive late in the weekend or early next week. Model guidance shows good agreement through Sunday, but for Monday-Wednesday of next week the 00 UTC ECMWF/Canadian ensembles, the 00 UTC Canadian, and especially the 00 UTC ECMWF digs the cooling/unsettling upper trough much further west into the West/Rockies while the GFS/GEFS are quite a bit more progressive and dug over the central Plains. I still believe that the forecast track of current west-Pacific Typhoon Maysak northward into Korea/NE Asia will act to enhance downstream flow amplification over the Pacific/Alaska then CONUS. Accordingly, the WPC medium range product suite was primarily derived from the 00 UTC ECMWF ensemble mean. This solution represents a composite of the solutions that dig more energy into the West/Rockies. It is not as robust as the closed trough solutions of the 00 UTC ECMWF and especially now with the 12 UTC ECMWF. It's not all apples-apples, but the newer 12 UTC GFS/Canadian/UKMET and GEFS have overall trended westward. In this pattern, heat will remain in place over the Southwest U.S. for much of the period and may strengthen into the weekend and surge northward into the Pacific Northwest. High temperatures well into the 90s are forecast for the hottest locations over the interior Northwest, before moderating early next week. Meanwhile expect a rush of much below normal post-frontal temperatures, especially through the Rockies/N-central states by next week. Enhanced snows will also be possible across the central/northern Rockies next week as per the latest winter weather outlook. The best chance for organized heavy rainfall during this period may develop from the south-central Plains toward the upper Midwest as the cold front associated with the first surge of cool air and moisture return from the Gulf lifts north and interacts with the slowing boundary, but there remains quite a bit uncertainty with axis specifics. Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml