Extended Forecast Discussion NWS Weather Prediction Center College Park MD 313 PM EDT Wed Jun 09 2021 Valid 12Z Sat Jun 12 2021 - 12Z Wed Jun 16 2021 ...Much above normal temperatures and record/dangerous heat this weekend into early next week across much of the interior West/Northern Plains... ...Extreme heat possible for the Southwest next week... ...Overview... Upper pattern is forecast to amplify along 105W this weekend into early next week, promoting warm/hot temperatures over much of the West and northern High Plains that may near or break daily records. Troughing exiting New England will dig back into the East next week supporting a couple cold frontal passages and a chance of showers/storms. A Pacific front will push into the Pacific Northwest early next week and head into Canada. ...Guidance/Predictability Evaluation... Through the 00Z/06Z cycle, the models/ensembles were in reasonable agreement and offered average to above average predictability and consistency in the longwave pattern evolution. This includes the upper flow amplification driven by near +3 sigma 500mb height anomalies via a closed 594+ dm upper high into the Four Corners region. The largest model spread existed with downstream troughing for the Great Lakes into Northeast next week. With such strong upstream ridging, the deeper troughing has become a clearer signal and preferred pattern but the depth and progressiveness remain uncertain. Upstream energy amplitude/track and interactions with shortwave energy coming out of Hudson Bay lower confidence by the middle of next week. Over the Gulf, a weakness between the Southwest and NW Caribbean ridges/highs will take a feature southwestward into Mexico, perhaps enhancing some rainfall over the open waters. Utilized a blend of the deterministic guidance (GFS/ECMWF/CMC/UKMET) to start, followed by increased weighting of the GEFS mean and ECMWF ensemble mean by days 6-7 (next Tue/Wed). 13Z National Blend of Models was a good staring point for temperatures and other surface grids but a multi-model/ensemble blend was used for QPF. This maintained good continuity from the overnight progs. ...Weather Highlights/Hazards... The amplification of the upper ridge over the central U.S. is expected to bring another round of much above normal to record warm/hot temperatures to the northern Rockies and northern Plains late this weekend and early next week. Temperatures over the Southwest may approach and exceed records as well next week with dangerously high temperatures into the 110s. Temperatures may be 10-25F above normal with some triple-digit readings possible as far north as central/eastern Montana Monday and Tuesday. Nighttime lows will also remain warm for the region and likely stay 10F to 15F above normal for the middle of June. 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. Fracasso/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 possible across portions of the Tennessee Valley. - Flooding occurring or imminent across portions of the Lower Mississippi Valley and the Southern Plains. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Sun-Wed, Jun 13-Jun 16. - Excessive heat across portions of the Northern Plains and the Northern Rockies, Mon-Tue, Jun 14-Jun 15. - 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 Northern Great Basin, the Upper Mississippi Valley, and the Southwest, Sun-Wed, Jun 13-Jun 16. - Much above normal temperatures across portions of the Northern Rockies and the Northern Great Basin, Sun-Tue, Jun 13-Jun 15. 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