Extended Forecast Discussion NWS Weather Prediction Center College Park MD 111 PM EDT Sat Aug 15 2020 Valid 12Z Tue Aug 18 2020 - 12Z Sat Aug 22 2020 ...Dangerous heat for much of the West through next week... ...Overview... The synoptic pattern over the CONUS through the medium range period (Tuesday-Saturday) is expected to feature persistent, strong upper ridging over the Southwest while troughing remains over the Ohio, Tennessee, and lower Mississippi River Valleys. This will result in well above normal temperatures, potentially record setting, from portions of the Pacific Northwest and Intermountain West southward through the Colorado River Valley and Southwest. Regarding rainfall, a stalled frontal boundary from the Gulf Coast and along the eastern seaboard will be the main focus for periods of showers and thunderstorms while lighter amounts are forecast across the Upper Midwest along another frontal boundary. ...Guidance/Predictability Assessment... The latest model guidance exhibited average to above average agreement and forecast consistency this cycle such that a near equal blend of the available deterministic guidance (00Z ECMWF/CMC/UKMET and 06Z GFS) was utilized for days 3-5. The biggest model differences lied across the Gulf of Alaska where the deterministic and ensembles showed higher spread as an upper low is forecast to move near British Columbia and Washington. The GFS/ECMWF and its ensemble means GEFS/ECENS were heavily used for days 6-7 with the lower confidence. ...Weather/Hazard Highlights... Forecast temperatures still suggest record temperatures for daily maxes and mins, mostly confined to the Desert Southwest but could include portions of the Pacific Northwest and Intermountain West. Many locations will only drop into the 80s for the Desert Southwest while daytime temperatures in the 100s will be common across the Great Basin while 110s to low 120s are expected in the lower deserts into Death Valley. Little to no rainfall is expected under the upper high. With troughing over the East, showers/storms will be favored over the Southeast especially in the afternoon. Moisture may surge into the Mid-Atlantic midweek as the front wanders along the coast. Northern stream troughing will bring in cooler than normal temperatures to portions of the Plains and mid-Mississippi Valley through the week with the best rainfall chances over the Upper Midwest. Fracasso/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