809 FXUS02 KWBC 021945 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 345 PM EDT Sun Aug 2 2026 Valid 12Z Wed Aug 05 2026 - 12Z Sun Aug 09 2026 ...Heat wave continues through the week across the Southwest and Intermountain West, expanding northeastward with time... ...Overview... The upper ridge causing excessive heat atop the Southwest midweek will gradually intensify and expand north and east late week into next weekend, bringing hot temperatures across the Intermountain West to Plains and potentially the South. Meanwhile, a handful of frontal systems in the central and eastern U.S. will trigger scattered showers and thunderstorms there, with monsoon convection in the Southwest as well. ...Guidance/Predictability Assessment... Models show good agreement on the large scale pattern evolution through the period, which features a northern stream trough through the north-central U.S. and a sprawling southern tier ridge. The main focus of uncertainty continues to be with the positions of various energies aloft within the broader trough, especially the latter part of the week and into the weekend. Possibly a couple of rounds of weak energy moving into the Northwest also show some variability. Recent trends have been for the peak values of the upper ridge (594dm at 500mb) to stay separate in the Southwest and farther east with a subtropical Atlantic ridge with some weak energy in between them. Overall, there are not really considerable outliers with the pattern. Thus the WPC forecast used a blend of deterministic guidance for the early part of the period, but used gradually increasing proportions of ensemble means as the period progressed to help smooth out increasing uncertainty. This maintained good continuity with the previous forecast. ...Weather/Hazards Highlights... For midweek, a slightly weaker upper ridge will allow for lessening HeatRisk across the Southwest compared to the short range period, though Moderate HeatRisk will still be widespread with isolated Major and Extreme values. Heat should build gradually northward across the Intermountain West and Rockies to the High Plains, as well as eastward in the Mid-South as the upper ridge expands. See Key Messages issued by WPC for this event for additional information regarding this long lasting and dangerous heat wave. After one more cool day in the north-central U.S. Wednesday, temperatures across the northern tier and into the East should be generally near average most of the period. A reasonably strong front will push into the Midwest and Central Plains by Wednesday and trigger a corridor of potentially heavy rain and thunderstorms along and ahead of it. Meanwhile, weak frontal boundaries will allow for showers and thunderstorms to be scattered across the East, with some locally heavy to excessive rainfall possible there as well. These interacting features should allow for additional rounds of rain and storms across the north- central to eastern U.S. through late week as the mean frontal boundary may stall for a bit. Elsewhere, monsoonal convection is likely for Arizona and New Mexico in particular, with scattered convection occasionally reaching portions of Utah and Colorado. The remainder of the West into the Northern Plains should be mostly dry during the period. Tate/Santorelli 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 $$