Extended Forecast Discussion NWS Weather Prediction Center College Park MD 249 AM EDT Mon Aug 31 2020 Valid 12Z Thu Sep 03 2020 - 12Z Mon Sep 07 2020 ...High heat rebuilds over the West next week... ...Weather/Hazard Highlights... The weather pattern across the CONUS mid to late week and into next weekend is expected to feature an upper level ridge over the western U.S. while troughing develops over the central/eastern US. This will support much above normal temperatures from the Desert Southwest (110-120F daily highs) through the west coast and portions of the Pacific Northwest. Conversely, a strong cold front working through the Northern Plains, Great Lakes, and East Coast will usher in drier, less humid conditions mid to late week. By next weekend, there remains an unusually strong guidance signal for additional flow amplification across the Pacific/Alaska that works downstream into Canada and the lower 48 states. This seems related to a downstream ripple effect from the concurrent northward forecast track of Typhoon Maysak from the west tropical Pacific to inland northeast Asia. This could result in amplified upper trough digging into the north-central U.S.. This would result in colder temperature profiles than shown in the NBM. WPC guidance shows potent post-frontal high pressure into the region, but probably underestimates cooling that in particular may allow a risk of northern Rockies snows given flow support in this scenario. ...Guidance/Predictability Assessment... Increasing signal and forecast confidence for a highly amplified flow pattern developing 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 primarily composed of the 12Z ECMWF/UKMET/CMC with some components of the 18Z/12Z GFS, using less of the 18Z GFS which had some timing/speed issues in the mid/late portions of the forecast period. With some decreasing forecast confidence by day 6/7, the ECENS was primarily used. 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