Extended Forecast Discussion NWS Weather Prediction Center College Park MD 318 AM EDT Fri Jul 29 2022 Valid 12Z Mon Aug 1 2022 - 12Z Fri Aug 5 2022 ***Major heat wave likely from the Northern Plains to the Upper Midwest early next week*** ***Monsoon remains active across the Southwestern U.S. with additional flooding potential on Monday*** ...Overview... A pattern change is forecast to evolve across the northwestern U.S. for the beginning of next week as an upper level trough and associated cold front bring welcomed relief from the intense heat wave expected in the short range period. The upper ridge responsible for this heat wave should cross the central/northern Plains and then the Midwest going into the middle of the week, and even affecting parts of the East Coast region by Thursday. The monsoon is expected to remain active across the Four Corners region with additional heavy showers and storms at times. ...Guidance Evaluation/Predictability Assessment... Model differences become apparent as early as Monday regarding the placement and evolution of the trough crossing the Pacific Northwest, with the latest 00Z run of the GFS east of the CMC/ECMWF/ECENS, whereas model agreement is good across the central and eastern U.S. for this time. Forecast confidence decreases to below average by the Wednesday to Friday time period as the western trough introduces additional uncertainties in the models. The 00Z ECMWF is at odds with the GFS and even the CMC across the Northern Plains for mid-week, and this out-of-phase problem persists going into the end of the week across the Great Lakes and Ohio Valley region. Therefore, significant adjustments to the forecast are likely in future updates as the overall model signal becomes clearer. For the WPC forecast, there was good agreement among the GFS/UKMET through Tuesday to merit their inclusion in the model blend, and then increasing the weighting of the ensemble means while still maintaining some of the 12Z ECMWF. ...Weather/Hazards Highlights... The heat wave in the Northwest/Great Basin is forecast to abate considerably going into Monday and especially Tuesday, with the heat axis shifting east ahead of an upper trough approaching the Pacific Northwest. Eventually, the anomalous heat shifts east across the northern and central Plains through the first half of next week, where daytime highs could once again approach or exceed 100F in many locations. Temperatures should also be on the rise from the Ohio Valley into the Northeast as heights begin to build through the middle to end of next week. Meanwhile, slightly above normal heat and humidity continues south of a frontal system over the nation's mid-section, continuing the record hot summer for much of the southern Plains and Southeast through much of next week. Heavy rain remains a threat across parts of the central and southern Appalachians and western foothills, where a Slight Risk of excessive rainfall remains for Day 4. However, the latest indications suggest the overall rainfall intensity should wane after Sunday, although the ground will be highly saturated and thus vulnerable to any additional rainfall. Persistent monsoonal moisture will continue to support diurnally driven heavy showers and storms with locally excessive rainfall over an already very soggy Southwest through the middle of next week. Hamrick/Jackson 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml