Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Sat Jun 29 2024 Valid 12Z Tue Jul 02 2024 - 12Z Sat Jul 06 2024 ***Hot and humid conditions for much of the Southern U.S., and heat increases across California and the Desert Southwest*** ...General Overview... Multiple shortwave passages across the northern tier of the nation will fuel scattered to numerous showers and storms for much of next week, particularly across the Midwest and portions of the Central Plains where the heaviest rainfall is likely to be midweek. Heat and humidity will continue to make weather headlines across much of the southern tier states as a strong ridge of high pressure aloft governs the overall weather pattern, and heat also expands across much of California and the lower elevations of Arizona and southern Nevada as the upper ridge builds across the West by the end of the forecast period. There will also be copious moisture in place across much of the Southern Rockies that will fuel scattered storms. ...Guidance/Predictability Assessment... The 00Z model guidance suite is in good synoptic scale agreement for the beginning to middle of the week, and a general model compromise suffices as a good starting point in the forecast process. The NBM appeared a little too light with QPF across the Four Corners region with respect to the monsoon, so these values were raised roughly 20-30 percent. Forecast uncertainties increase the most across the northwestern U.S. for the second half of the week, with recent runs of the GFS/GEFS still at odds with the ECMWF/CMC solutions regarding the upper ridge placement and the downstream trough across the Northern Rockies and the Dakotas. The GFS has been more progressive with that trough across the Northern Plains, but the differences are smaller than they were yesterday at this time. Upon examination of the machine learning guidance, there was better support for the CMC/ECMWF solutions for Friday and into next Saturday, so the 18Z GFS was tapered down by this time, and there was more of the ECENS than the GEFS used as a result. ...Weather/Hazards Highlights... It generally remains the case that widespread showers and storms are expected to be ongoing across portions of the Upper Midwest and western Great Lakes region on Tuesday ahead of a frontal boundary and an upper level impulse moving through the region. Although the overall forecast rainfall totals are currently expected to be in the 1-2 inch range from central Iowa to southern Wisconsin, this would be falling on highly saturated grounds in many cases, which would be an aggravating factor when it comes to flooding potential. Therefore, the Slight Risk remains valid for the new Day 4 ERO across this region. Marginal and Slight Risk ERO areas are planned for the new Day 5 outlook Wednesday as the signal for a main axis of heavy convection drops southward to include eastern Kansas, much of Missouri, and into central Illinois. Monsoonal flow into the Southwest states will continue the daily threat for showers and storms through much of the period. Marginal risks remain in place across parts of Arizona and New Mexico for both the Day 4 and 5 EROs, with the potential for upgrades to a Slight Risk in subsequent updates during the short range forecast period. There may be some southern suppression of this moisture going into the end of the week and confine the greatest coverage of convection across southeast Arizona and southern New Mexico. It will continue to remain hot and humid across the Southern U.S. for much of next week, with the hottest conditions centered across Texas and Oklahoma where triple digit high temperatures are likely. Some of this heat likely reaches the Mid-Atlantic region after a brief cool-down by the end of the week with highs returning to the 90s amid increasing humidity levels. It will also be getting hotter for the inland lower elevations of California and into the Arizona Deserts with widespread 100-110 degree readings likely, and locally higher for the normally warmer locations. Hamrick 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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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 https://www.wpc.ncep.noaa.gov/#page=ovw