Extended Forecast Discussion NWS Weather Prediction Center College Park MD 457 PM EDT Fri Jul 09 2021 Valid 12Z Mon Jul 12 2021 - 12Z Fri Jul 16 2021 ...Excessive Southwestern Heat Persists into Next Week... ...Midwest Heavy Rainfall Threat Mid-Later Next Week... ...Pattern Overview with Weather Highlights/Hazards... The heat wave now underway under upper ridging will continue for the Great Basin to CA and the Southwest into early-mid next week with temperatures 10-20F above normal. Several daily high temperature records are likely through Tuesday/Wednesday in these areas. The model consensus is leading to gradually lowering heights with a developing modest northwest US trough, with the highest heights shifting south into southern CA/AZ as more progressive/flatter flow emerges over the U.S. northern tier. Lingering upper ridging over the western Atlantic and into the Southeast may support above normal temperatures next week from the Mid-Atlantic to the lower Great Lakes and into the Northeast. This includes the Washington, DC to Baltimore, Philadelphia, and New York City corridor. The forecast does indicate some potential for temperature moderating showers/thunderstorms over the Southwest/Southern Rockies next week with pockets of enhanced 700 mb relative humidity in place to support diurnal activity with instability peaking each afternoon/evening. However, this could also fuel additional local downpour and terrain enhancing runoff issues. There is also a growing signal for the emergence of a multi-day heavy rainfall/convective repeat pattern into the Midwest Wednesday-Friday as shortwave energies reinforce upper troughing over the north-central U.S. and as moisture and instability pool along/ahead of a wavy front. Main focus may shift from the Upper Midwest to the Mid-MS/OH Valleys with slow system translation. This offers runoff threats with the region slated for chances of heavy rainfall over short range time frames. ...Guidance/Predictability Evaluation... Model and ensemble forecast spread into next week remains low in a slowly evolving pattern with a 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. Latest 12 UTC guidance overall still maintains this medium range solution. 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 Lower Mississippi Valley and Tennessee Valley, Mon, Jul 12. - Heavy rain across portions of the Middle Missouri Valley and the Middle and Upper Mississippi Valley, Wed, Jul 14. - Heavy rain across portions of the Central Plains, Middle Mississippi Valley, Ohio Valley, and Great Lakes, Thu-Fri, Jul 15-Jul 16. - Flooding possible across portions of the Northeast, the Middle Mississippi Valley, the Mid-Atlantic, the Upper Mississippi Valley, the Southeast, the Great Lakes, and the Ohio 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 Southwest, the Central and Southern Great Basin, and the Central Rockies, Mon-Tue, Jul 12-Jul 13. - Excessive heat across portions of the Interior Pacific Northwest, Mon-Wed, Jul 12-Jul 14. - Excessive heat across portions of the Central and Northern Great Basin, Mon-Fri, Jul 12-Jul 16. - Much above normal temperatures across portions of the Northern High Plains, Thu-Fri, Jul 15-Jul 16.