Extended Forecast Discussion NWS Weather Prediction Center College Park MD 334 PM EDT Thu Jun 10 2021 Valid 12Z Sun Jun 13 2021 - 12Z Thu Jun 17 2021 ...Record to dangerous heat this weekend into early next week across much of the interior West and the northern Plains... ...Extreme heat possible for the Southwest next week... ...Overview... Anomalously strong upper ridge building and amplifying through the central U.S. into next week will continue the much above normal temperatures across much of the West into the northern Plains. Record heat will be possible early next week from the Southwest to the northern Plains where the duration of the heat will become excessive and dangerous. Troughing exiting New England will dig back into the East next week supporting reinforcing cool air intrusions from Canada and a chance of showers/storms. A Pacific front will likely push into the Pacific Northwest early next week and should be moving across the northern Plains by the latter part of next week. ...Guidance/Predictability Evaluation... Guidance from major models and ensembles continue to show very good agreement for an amplified flow pattern gradually progressing eastward across the CONUS during the medium range period (Sunday-Thursday). A 594+ dm upper high expanding across the Four Corners and central Rockies toward the northern Plains next week will ensure a heat wave to encompass areas from California through much of the northern Plains. Meanwhile, models continue to indicate run-to-run variability of the timing and amplitude of shortwave energy digging across the Great Lakes to the Northeast, and a general trend for a more amplified trough to potentially close off over Quebec by Tuesday onward. The ECMWF continues to show much less-defined reinforcing cold fronts dipping across the Northeast than the GFS and CMC. The WPC medium-range forecast this cycle was derived from a composite blend of the 00Z ECMWF/EC mean, 06Z GFS/GEFS, with a smaller contribution from the 00Z CMC/CMC mean. More of the ensemble means were incorporated for Days 5-7 to handle the uncertainty over the Northeast. ...Weather Highlights/Hazards... The upper ridge over the central U.S. will keep temperatures much above normal from portions of the Southwest through the northern Plains late this weekend through much of next week. Departures from normal of 15F to 25F will be common with daily records likely to be set Monday-Wednesday. High temperatures well into the 110s will be possible across the Southwest while upper 90s to lower 100s will be possible from Utah into portions of the northern Plains as well as the lower elevations of the northern Rockies. Little relief at night is expected with nighttime lows 10F to as much as 20F above normal. The duration of this type of heat, especially for areas in the northern tier unaccustomed to prolonged heat waves, will become dangerous for sensitive groups. Elsewhere across the CONUS, temperatures are expected to be near to slightly above normal, perhaps a bit below normal over the Great Lakes into the Northeast next week behind a cold front. The strong/dominant upper ridge over the central CONUS will keep much of the area void of significant or heavy rainfall -- the exceptions being over the Northwest as a front moves in this weekend and possibly along the Gulf Coast to Southeast U.S. late this weekend into early next week where a frontal boundary stalls and lingers. Finally, the National Hurricane Center is monitoring the southwestern Gulf of Mexico for the potential for tropical cyclone development toward the latter part of next week. Kong/Taylor Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley. - Flooding likely across portions of the Tennessee Valley. - Excessive heat across portions of the Central Great Basin, the Northern Rockies, the Central Rockies, California, the Northern Great Basin, and the Southwest, Sun-Thu, Jun 13-Jun 17. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Wed-Thu, Jun 16-Jun 17. - Excessive heat across portions of the Central Rockies, the Central Plains, the Upper Mississippi Valley, the Northern Plains, and the Northern Rockies, Sun-Wed, Jun 13-Jun 16. - Much above normal temperatures across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Middle Mississippi Valley, the Northern Great Basin, the Upper Mississippi Valley, the Great Lakes, and the Southwest, Sun-Thu, Jun 13-Jun 17. 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