Extended Forecast Discussion NWS Weather Prediction Center College Park MD 247 AM EDT Fri Aug 14 2020 Valid 12Z Mon Aug 17 2020 - 12Z Fri Aug 21 2020 ...Dangerous heat for much of the West early next week... ...Overview... A strong upper high will meander near the Desert Southwest next week while troughing will retrograde slightly in the East. Well above normal temperatures will approach and exceed records for many locations from Idaho southward through the Colorado River Valley. Rainfall will be focused over the Southeast around a stalled front with lighter amounts over parts of the Rockies and Upper Midwest. ...Guidance/Predictability Assessment... With good ensemble agreement overall, the deterministic models showed acceptable clustering so that a blended approach was used as a starting point to the forecast. Uncertainty increased atop the upper high with incoming Pacific shortwaves and how they flatten the top side of the ridge over the Northwest and southern Canada. In the East, lead troughing will exit northeastward but be reinforced by the end of the week, tugging the axis westward. GFS runs may have been on the more aggressive side overall so the ECMWF was weighted a bit more than the GFS. The UKMET/Canadian offered some detail to the forecast though each was less consistently clustered near the ensembles means. ...Weather/Hazard Highlights... Upper high will promote record heat for many areas west of the Rockies while some showers/storms may fire on the east side of the Rockies over Colorado and New Mexico with limited moisture. Record high max and min temperatures will persist over the Desert Southwest and surrounding areas through the Great Basin and inland areas of California through at least the first half of the week, perhaps cooling a bit by next Thu/Fri. Temperatures in the 100s will be common with highest readings over 120F in 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 westward to Texas especially in the afternoon. This may drift northward 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 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