Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 AM EDT Thu Sep 03 2020 Valid 12Z Sun Sep 06 2020 - 12Z Thu Sep 10 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... The synoptic pattern over the medium range period starts with average predictability and confidence per the latest agreement in the deterministic and ensemble guidance however quickly diverges significantly by day 5 through day 7 with respect to the digging/amplifying trough axis over the Rockies to central US. From a sensible weather perspective, large temperature anomalies are the main headline however some axis of heavier precipitation will be possible, particularly by day 6/7 somewhere across the central US. The ECMWF remained the most westward solution, digging the trough well into the Great Basin and closing off at the mid/upper levels by day 6/7. Meanwhile, the GFS digs similarly to the ECMWF but is progressive and swings the trough toward the Mid-MS River Valley by day 7. The CMC remained in the middle and was sort of a compromise and also mirrored the ECENS to some degree. The GEFS was still faster than the consensus. Teleconnections based on the strong positive anomaly over western B.C. supports the digging trough well into the south-central US with some favoring to the west, so this cycle the WPC blend continued to utilize heavily the ECMWF and ECENS (day 5-7) with some inclusion of the CMC as a compromise to the possibility of a faster GFS solution verifying, given the much below normal forecast confidence late in the period. 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/Taylor 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