Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Sat Jun 29 2024 Valid 12Z Tue Jul 02 2024 - 12Z Sat Jul 06 2024 ...Hazardous heat over the South next week spreads to parts of the East/Southeast and California/Southwest into the Holiday period... ...Heavy convective rainfall focus for the Midwest next week... ...Pattern Overview... An established pattern will generally continue as 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 daily storms. ...Guidance/Predictability Assessment... Model and ensemble forecast spread remains lower than normal through medium range time scales in a pattern with above average predictability, albeit still with standard smaller scale weather feature uncertainties that tend to be muted by a guidance blending process. The WPC product suite was primarily derived for the Tuesday- Thursday/July 4th timeframe from a blend of well clustered guidance of the 06 UTC GFS and 00 UTC ECMWF/UKMET/Canadian along with the generally compatible 13 UTC National Blend of Models (NBM) and WPC continuity. Opted to switch the favored blend to best clustered guidance from the GFS/ECMWF and GEFS/ECMWF ensemble means along with the NBM for later next week amid slowly growing variances at these longer time frames. ...Weather/Hazards Highlights... 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. Locally heavy convective downpours may fall on saturated grounds in some cases, which would be an aggravating factor when it comes to flooding potential. Therefore, the Slight Risk remains valid for the Day 4 ERO for this region. Marginal and Slight Risk ERO threat areas also remain for the 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. Activity should remain broadly robust over the Midwest through the Fourth leading to possibly ample runoff issues, but focus may gradually ease and slowly shift southward and eastward across much of the central and eastern U.S. late next week/weekend with less certain flow/frontal progression. 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/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 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