Extended Forecast Discussion NWS Weather Prediction Center College Park MD 320 PM EDT Fri Aug 14 2020 Valid 12Z Mon Aug 17 2020 - 12Z Fri Aug 21 2020 ...Dangerous heat for much of the West through next week... ...Overview... A strong upper high centered over southern Utah Monday looks to drift south into Arizona through next week. The ridge extending from this high up the Rockies and into Alaska Monday will be topped by shortwaves ejecting from a Gulf of Alaska, particularly in the middle of next week when the first low ejects east, but restrengthens late next week as the next Gulf of Alaska low settles in. Well above normal temperatures will approach and exceed records for many locations from Oregon/Idaho southward through the Colorado River Valley and across the Desert Southwest. Rainfall will be focused along a stalled front from the Northeast, along or off the Southeast coast and along the Gulf Coast with some transient precip in the Upper Midwest mid to late next week. ...Guidance/Predictability Assessment... With good ensemble agreement overall, the deterministic models showed acceptable clustering so that a blended approach was used through Day 5. Uncertainty increases midweek atop the upper high with incoming Pacific/Gulf of Alaska shortwaves and how they flatten the top side of the ridge over the Northwest and southern Canada. The GFS is more aggressive with the energy from the Pacific and suppresses/shifted the ridge axis farther east than the rest of guidance. This scenario continues with the 12Z GFS. In the East, lead troughing will exit northeastward into eastern Canada as a gyre sets up over Hudson Bay which will shift the trough axis westward. By Day 5 the 06Z GFS was reduced in the blend in favor of the 00Z ECMWF and 00Z ECENS/06Z GEFS (ensemble means increase in the blend through Day 7). The 00Z UKMET/Canadian were close enough to the consensus to be included through Day 5. ...Weather/Hazard Highlights... The upper high/ridge over The West 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 Great Basin, Desert Southwest and inland areas of California through next week. Temperatures in the 100s will be common across the Great Basin with 110s in teh Desert Southwest and 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 looks 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. Jackson 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 Hazards: - Heavy rain across portions of the Southeast, the Mid-Atlantic, and the Southern Appalachians, Tue-Wed, Aug 18-Aug 19. - Heavy rain across portions of the Southeast, Thu-Fri, Aug 20-Aug 21. - Flooding possible across portions of the Upper Mississippi Valley and the Northern Plains. - Excessive heat across portions of the Pacific Northwest, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Mon-Tue, Aug 17-Aug 18. - Excessive heat across portions of California, the Central Great Basin, the Pacific Northwest, the Northern Rockies, and the Northern Great Basin, Mon-Wed, Aug 17-Aug 19. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Mon-Thu, Aug 17-Aug 20. - Much above normal temperatures across portions of the Central Rockies and the Central Great Basin, Mon-Thu, Aug 17-Aug 20. 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