540 FXUS02 KWBC 050654 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 254 AM EDT Sun Jul 5 2026 Valid 12Z Wed Jul 08 2026 - 12Z Sun Jul 12 2026 ...Major to Extreme Heatwave to settle across the Southern Tier this week... ...Pattern Overview... Broad upper-level ridging is forecast to build over the Southern U.S. this week while transient shortwaves propagate through the Great Lakes and Northeast/Mid-Atlantic. The southern ridge will support a major heatwave initially over the South/Southeast then building into the Southwest/Great Basin. Troughing along the U.S.-Canadian border will promote diurnal showers and thunderstorms from the Northern Plains to the Northeast, with a focused risk for heavier rain over the Upper Midwest into the Great Lakes Tue-Wed. Troughing over the Northeast Pacific will maintain near to below average temperatures in the Pacific Northwest. ...Guidance/Predictability Assessment... Models are in reasonably good agreement on the synoptic pattern beginning this Wednesday and continuing through the weekend. Thus, a general model blend consisting of the available deterministic and Ai guidance were used through day 5, before gradually incorporating the ensemble means through the end of the period. The UKMET was not included in the blend due to an overamplified trough over the Midwest compared to consensus. ...Weather/Hazards Highlights... A major heat wave is expected to expand beneath a growing upper- level ridge in the Central/Southern U.S.. This heat wave will spread from the Southeast to the Southern Plains and into the Central Rockies by the weekend. Heat indices between 105-115 are expected across the South. Troughing in the Northeast/Mid-Atlantic will support continued hot/moist southerly flow into the Florida Peninsula, in particular, where there's a growing concern for extreme heat risk beginning on Wednesday and continuing into the weekend. No overnight relief from hot temperatures will affect anyone without adequate cooling/hydration as well as health systems, industries and infrastructure. Surface waves and attendant fronts draped across the Northern Plains and Upper Midwest/Great Lakes will be the focus for scattered thunderstorms on Wednesday. Well above normal moisture (>90th percentile) and instability along the front could combine to produce heavy rainfall/flash flooding, but weak shearing will likely mitigate a severe weather threat. Rain showers and thunderstorms will shift into the East Coast later in the week and into next weekend. Lastly, monsoonal moisture may start to increase over at least Arizona late next week into the weekend as the upper high drifts a bit farther north into Utah. Kebede 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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw $$