Extended Forecast Discussion NWS Weather Prediction Center College Park MD 242 PM EDT Sat Jun 19 2021 Valid 12Z Tue Jun 22 2021 - 12Z Sat Jun 26 2021 ...Heat intensifies later next week over the interior Northwest toward record levels... ...Midweek heat for portions of the Plains... ...Overview... Upper ridging is again forecast to build/strengthen into parts of the West next week as troughing along the West Coast slowly drifts offshore. This will allow another stretch of warm/hot weather and records highs to expand over the Pacific Northwest southward to the Desert Southwest by late in the week. In turn, this will promote downstream troughing over the Great Lakes/Midwest/Northeast as another frontal boundary pushes through the region with showers and storms. ...Guidance/Predictability Evaluation... Through the 00Z/06Z cycle, the models and ensembles showed reasonable clustering with the exiting eastern trough (containing Claudette just offshore) and the next Pacific/Canadian trough forecast to dig through southern central Canada late in the period. Despite some detail differences in the GFS/ECMWF/Canadian in timing and strength, a blended solution sufficed with a bit more weighting to the ECMWF as it paired better with its ensemble mean and to most extent the GEFS mean. This ECMWF-led solution showed a bit more amplitude than continuity but was supported by recent trends. Even in the ensemble mean solution, 500mb heights are forecast to build to over +3 sigma in the PacNW by next weekend, suggesting well above normal temperatures and likely ran expanding area of record highs. ...Weather Highlights/Hazards... Recent record-breaking heat over the Southwest/California is expected to ease by the start of the medium range (Tue). As the upper low just off northern California weakens, strong ridging from the Pacific and from Texas will build over the West, allowing temperatures to climb to 15-25 degrees above normal in Washington/Oregon late in the period, and more generally at least 5-10 degrees above normal along and west of the Rockies. Record highs are likely for an expanding area late in the week as temperatures near and over 100F will be possible in interior sections of the West into eastern Washington. Rainfall will be little to none throughout the region. In the East, exiting trough with Claudette will sweep organized rainfall into the Atlantic, ensuring a brief respite from the active weather. Temperatures will be near to below normal east of the Mississippi for 1-2 days before moderating. By later next week, troughing out of Canada will carry another cold front southeastward as a warm front lifts through and out of the southern Plains, inviting moisture northward. Showers and storms will likely increase in coverage and intensity later next week along and ahead of the front and near areas of low pressure, focused over the Upper Midwest/Corn Belt into the Ohio Valley. Fracasso 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 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