733 FXUS02 KWBC 061856 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Sun Jul 6 2025 Valid 12Z Wed Jul 9 2025 - 12Z Sun Jul 13 2025 ...Hazardous heat and humidity continues for parts of the East while the heat builds over the West... 19Z Update: The 12Z model guidance starts off in excellent agreement across the Continental U.S. on Wednesday, with a multi- deterministic model blend as a starting point in the forecast process. This general philosophy holds true going into Thursday as well, and models have trended towards a stronger shortwave trough and potential closed low over the Dakotas and Minnesota to close out the work week. The 00Z CMC was more out of line with the model consensus at the time of fronts/pressures preparation, but the new 12Z run is better. Model differences become more pronounced across southern Canada going into next weekend, and the ECMWF becomes stronger with an upper ridge near the Pacific Northwest coast by Sunday. The ensemble means were gradually increased to about half by this time. The previous forecast discussion is appended below for reference. /Hamrick ------------------ ...Pattern Overview... The large scale pattern will transition from being quasi-zonal to having an upper ridge over the West/Southwest with troughing over the Great Lakes into the Northeast. This change will be bolstering widespread heat across the Southwestern states. A low pressure system will advance through the northern/central states toward the Northeast and will be the focus for scattered showers and thunderstorms. ...Guidance/Predictability Assessment The latest guidance has above average confidence for hazardous heat with the upper ridge building over the west and for multiple impulses to track through the flow as troughing sets up over the Northeast. The main feature tracking from the eastern Pacific to the Northeast remains faster with the GFS/GEFS mean whereas the CMC is deeper with the closed low/trough exiting the Dakotas. The spread was still acceptable however weighting of those solutions were reduced later in the extended period. WPC utilized a combination of the OOZ ECMWF/GFS/Canadian/UKMET/ECMWF ensemble mean/GEFS mean, continuity and the NBM. ...Weather/Hazards Highlights... Showers and thunderstorms are expected to be focused in proximity to progressive cold fronts, stalled boundaries and round the upper high in the Southern Rockies. The wavy front into the eastern U.S. may be a focus for heavier rain and thunderstorms. This includes areas from the Corn Belt into the Midwest and Ohio Valley, Appalachians, Mid-Atlantic, and Northeast. There are Marginal Risks in place (level 1 of 4) for the ArkLaTex region on Day 4, for parts of the Dakotas and Upper Midwest on Day 5, and for portions of the Mid-Atlantic into North Carolina and the southern Appalachians for both days 4 and 5 for an axis of heavier rainfall that is likely south of a frontal boundary. Many locations will have daily maximums climbing well into the 100s at lower elevations across the Southwest and mainly dry conditions, except for perhaps far southeastern Arizona into New Mexico where some monsoonal moisture may be present. Experimental HeatRisk values may rise to Major or Extreme levels (3 out of 4 or 4 out of 4) from the California deserts into southern Nevada, Utah, and Arizona. Extreme Heat Watches have been raised for parts of Arizona through at least Thursday. Campbell 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 $$