Extended Forecast Discussion NWS Weather Prediction Center College Park MD 233 AM EDT Thu Aug 13 2020 Valid 12Z Sun Aug 16 2020 - 12Z Thu Aug 20 2020 ...Heat Wave with Record Temperatures for the dry West... ...Guidance/Predictability Assessment... Model and ensemble solutions seem well clustered days 3-5/Sun-Tue and a composite of GFS/ECMWF/UKMET runs seems to offer a reasonable forecast starting point along with the National Blend of Models. Amid gradually growing forecast spread days 6-7/Wed-Thu, the ECMWF clusters best with GEFS/ECMWF ensemble means with more persistent and stronger ridge continuity over the West in an amplifying pattern with overall above normal predictability. ...Weather/Hazard Highlights... A closed upper high centered over the southern Great Basin along with upper ridging from the southern Plains through the West will continue to inhibit monsoonal flow. Much above normal temperatures will build north with the ridge over the Intermountain West and West Coast to the Northwest. Heat wave temperatures will range 5-15 degrees above normal, upwards to 15-20 degrees above normal in the Northwest Sun-Tue. Record high max and min temperatures will persist over the Desert Southwest with temperatures up to 115-120 degrees. Additional record highs will spreads over the rest of the West in tandem with upper trough amplification off the West Coast. This will foster a continued dry pattern with frontal relief expected only for the Pacific Northwest next midweek. Meanwhile, amplified upper troughing settles over the east-central U.S.. Widespread showers and thunderstorms will gradually push through the Eastern Seaboard early next week as a wavy lead front/modest coastal low and a temperature moderating main front digs robustly down through the central and eastern U.S.. This may produce some local runoff issues, especially early period for the recently wet Mid-Atlantic. A wavy trailing front will settle through the Southeast and Gulf of Mexico back to the Plains/Rockies and focus additional bouts of convection, some strong to severe, into mid-later next week as impulses dig to the lee of the western ridge. 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