Extended Forecast Discussion NWS Weather Prediction Center College Park MD 244 AM EDT Tue Sep 01 2020 Valid 12Z Fri Sep 04 2020 - 12Z Tue Sep 08 2020 ...High heat rebuilds over the West late this week while shot of much cooler air arrives for the north-central U.S. early next week... ...Weather/Hazard Highlights... An amplifying upper level pattern is forecast to evolve over the CONUS, which will be the main driver for temperature anomalies during the forecast period. The Southwest U.S. ridge will persist and shift westward during the period and expand northward by day 6/7 as the ridge axis anchors over western North America. In fact, high temperatures soaring above the century mark will be increasingly common for the interior Valleys of California by this weekend; and by next Monday, record high temperatures may be established at many locations. Triple-digit high temperatures are also forecast for the hottest locations over the interior Pacific Northwest. Conversely, a digging deep trough is forecast over the central U.S. and Canada, bringing much below normal temperatures by late in the weekend and early next week. Daily readings could be 15-20F below normal and the first real push of autumn-like air for portions of the CONUS. Excessive precipitation is not expected to be widespread during the period but along/ahead cold fronts sweeping the control, some periods of showers/thunderstorms are expected. ...Guidance/Predictability Assessment... Increasing signal and forecast confidence for an amplifying flow pattern over the CONUS during the medium range period, featuring upper ridging over the western US with a deep longwave trough centered over the central US. The latest model guidance shows very good agreement with this idea and overall, the deterministic models had tight clustering through day 5/6 which bolstered the forecast confidence this cycle. The WPC blend was composed of a blend the 12Z ECMWF/CMC/UKMET and 18Z GFS through day 5 then followed by higher weights/inclusion of the latest ECENS/GEFS means. 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