Extended Forecast Discussion NWS Weather Prediction Center College Park MD 517 PM EDT Thu Jul 08 2021 Valid 12Z Sun Jul 11 2021 - 12Z Thu Jul 15 2021 ...Excessive Western Heat Persists into Next Week... ...Pattern Overview with Weather Highlights/Hazards... The ongoing heat wave under upper ridging will continue for the Great Basin to the Coastal Ranges and lower CO River Basin into next week with temperatures 10-20F above normal through Tuesday with locally higher readings possible. Several daily high temperature records are likely through Tuesday, primarily over the Great Basin through interior California to Arizona. There is a growing guidance signal suggesting slow moderation of the anomalous pattern through next week as flatter/more progressive flow increasingly emerges across southern Canada and the entire U.S. northern tier. There is also some rainfall relief potential over the Southwest/Southern Rockies with gradual moisture return next week. Meanwhile, expect a heavy rainfall threat to persist over the Midwest and focus over the lower MS Valley on Sunday as fueled by return/pooling Gulf Moisture and instability along with lingering upper trough support and surface frontal system passages. Then, by the middle of next week the next Midwest system looks to bring heavy rainfall potential back to the Upper Midwest which has been rather wet over the past few weeks. ...Guidance/Predictability Evaluation... Model and ensemble forecast spread into next week are low in a slowly evolving pattern with mean Midwest trough/low and the western ridge gradually suppressing into southern Cal and vicinity early next week. The WPC medium range product suite was primarily derived from a blend of well clustered guidance from the 06 UTC GFS/GEFS, 00 UTC ECMWF/UKMET/Canadian and ECMWF/NAEFS ensembles along with the 13 UTC National Blend of Models. This broad composite maintains good WPC continuity and acts to mitigate smaller scale guidance differences, especially over time with convective focus and for shortwave activity over the Northwest coming into the mean Midwest trough. Newer 12 UTC guidance overall maintains this medium range solution so far. Jackson/Schichtel 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 Hazards: - Heavy rain across portions of the Mississippi Valley, the Great Lakes, the Ohio Valley, the Tennessee Valley, and the Southern Plains, Sun, Jul 11. - Heavy rain across portions of the Lower Mississippi and Tennessee Valleys, Mon, Jul 12. - Heavy rain across portions of the Middle and Upper Mississippi Valley, Wed, Jul 14. - Flooding possible across portions of the Southeast and the Middle Mississippi Valley. - Flooding occurring or imminent across portions of the Southeast, the Middle Mississippi Valley, and the Southern Plains. - Flooding likely across portions of the Southeast and the Southern Plains. - Excessive heat across portions of California, the Interior Pacific Northwest, and the Southwest, Sun-Tue, Jul 11-Jul 13. - Excessive heat across portions of the Southwest, Sun-Mon, Jul 11-Jul 12. - Excessive heat across portions of the Great Basin and the Interior Pacific Northwest, Sun-Thu, Jul 11-Jul 15. - Much above normal temperatures across portions of the Northern Rockies and Northern High Plains, Sun-Mon, Jul 11-Jul 12.