Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Mon Jul 1 2024 Valid 12Z Thu Jul 4 2024 - 12Z Mon Jul 8 2024 ***Major heatwave expected for the lower elevations of California and the Desert Southwest next week, and remaining hot and humid for the south-central to southeastern states*** ...Overview... Multiple shortwave passages across the northern tier of the nation will fuel scattered to numerous showers and storms for the middle to end of the week, particularly across the Midwest and portions of the Central Plains/Middle Mississippi Valley where the heaviest rainfall is likely. 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 likely be some abatement in the thunderstorm coverage across the Southern Rockies after multiple days of flash flooding concerns. ...Guidance/Predictability Assessment... The 00Z guidance has a good overall depiction of the synoptic scale pattern for the end of the week, with improvement in the models with respect to the Western U.S. and the evolution of the upper ridge near the West Coast. The CMC is displaced some to the east with the ridge axis and farther inland compared to the model consensus. The updated forecast was based on a blend of the deterministic models early in the period, with inclusion and gradual increase of the GEFS and EC ensemble means to about half by Day 7/Monday. Hurricane Beryl is forecast to reach the Bay of Campeche by Friday evening based on the latest NHC track. The best model clustering, along with the ML guidance, shows Beryl being steered into northeastern Mexico next weekend. But there is some guidance that curves the system farther north into southern Texas, including the 00Z CMC that seemed to be a faster and northern outlier, and the 12Z JMA from yesterday, but those solutions are not currently favored. Beryl's track will continue to be monitored over the next several days, and see NHC's website for official forecasts. ...Weather/Hazards Highlights... By Day 4/Independence Day, the overall QPF signal in the guidance is looking more diffuse with scattered higher QPF maxima, so a broad Marginal Risk still seems to be the best way to go for now, with potential Slight Risk areas in future updates as the details become more evident. Farther north, additional mesoscale convective systems are likely to form and track through north-central parts of the country. A Marginal Risk is in place for parts of the Upper Midwest on Day 4, and then northern Wisconsin and the U.P. of Michigan for Day 5. Good support for lift should be present there with an incoming shortwave, but with less anomalous moisture compared to areas farther south. For the Day 5 period, a broad Marginal Risk area is planned from eastern Oklahoma to the Tennessee River Valley in the vicinity of a frontal boundary that will intercept a hot and humid airmass with plenty of moisture available. A cold front slowly pressing east will eventually spread thunderstorms to the Eastern Seaboard into the weekend, while more rounds of storms are possible in the central U.S. as well. It will continue to remain hot and humid across the Southern U.S. for the middle of the week and into next weekend, with the hottest conditions centered across the Southern Plains on Wednesday- Thursday where triple digit high temperatures are likely. The heat will abate somewhat there into late week and the weekend (but still feeling summer-like), while the Southeast to Mid-Atlantic should see temperatures and heat indices rising. It will also be getting very hot for the inland lower elevations of California and into the Arizona Deserts with widespread 105-115 degree readings likely, and locally higher for the normally warmer locations. Above normal temperatures by 10-20 degrees should stretch into Oregon and Washington late week into next weekend as well. 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