925 FXUS21 KWNC 071838 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT July 07 2026 SYNOPSIS: Highly amplified mid-level high pressure is forecast to develop across the western and central contiguous U.S. (CONUS) during week-1 and persist into week-2. While there is some uncertainty in the dynamical models regarding the westward progression of this feature and the extent of mid-level low pressure downstream in the East, a broad area of extreme heat is likely across the western, central, and southeastern CONUS throughout the period given the climatological peak of summer time heating. This pattern is also expected to enhance the monsoonal circulation, potentially bringing tropical moisture and a risk of heavy precipitation into parts of the southwestern CONUS. HAZARDS High risk of extreme heat across portions of the Northern Plains and Upper Mississippi Valley, Wed-Thu, Jul 15-16. Moderate risk of extreme heat across portions of the California Central Valley, Southwest, Great Basin, and the Rockies, Wed-Fri, Jul 15-17. Moderate risk of extreme heat across the Great Plains, Mississippi Valley, Southeast, and Carolinas, Wed-Fri, Jul 15-17. Slight risk of extreme heat across much of the western and central CONUS as well as the Southeast, Ohio and Tennessee Valleys, Great Lakes, and the southern Mid-Atlantic, Wed-Sun, Jul 15-19. Slight risk of heavy precipitation across portions of the Central and Southern Rockies and Desert Southwest, Tue-Fri, Jul 15-19. DETAILED SUMMARY FOR FRIDAY JULY 10 - TUESDAY JULY 14: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR WEDNESDAY JULY 15 - TUESDAY JULY 21: Multiple model ensembles depict anomalous ridging developing across the western and central CONUS around the middle of week-1 and persisting into week-2. While the ridge is predicted to peak in strength prior to the start of week-2, the 0z ECMWF and GEFS ensembles still depict a 595-596 dm ridge center at the outset of week-2. The challenge in today's forecast is the positioning of the ridge axis. The ECMWF ensemble continues to depict a more eastward orientation of the ridge, with enhanced positive 500-hPa height anomalies (greater than 60 meters) over portions of the Midwest. Conversely, the GEFS depicts more amplified troughing developing over eastern Canada which results in a quicker retrogression of the ridging over the western CONUS, and increasing northwesterly mid-level flow into the Upper Midwest and Ohio Valley favoring relatively cooler temperatures. The forecast leans more on the ECMWF due to recent model skill in persisting the previous heat wave across the eastern U.S. At the start of the period, extreme heat is forecast across much of the Great Plains and Mississippi Valley underneath the aforementioned ridge axis. In addition, enhanced subtropical ridging combined with above-normal sea surface temperatures over the eastern Gulf of America favor extreme heat across portions of the Southeast and Florida. The ECMWF ensemble indicates temperatures near or above 90 deg F across the Great Lakes and Ohio Valley early in week-2, with the ECMWF Probabilistic Extremes Tool (PET) depicting at least a 40 percent chance maximum temperatures exceed the 85th climatological percentile across the Upper Midwest. However, the GEFS is substantially cooler over these areas, as a frontal system moves through the region tied to troughing amplifying across eastern Canada. The GEFS solution would favor the largest extreme heat risk shifting farther to the west over the Great Plains and western CONUS. A high risk of extreme heat is posted across portions of the Northern Plains and the adjacent areas of the Upper Mississippi Valley, Jul 15-16, where skill weighted heat risk guidance indicates probabilities greater than 50 percent for heat index values to exceed 100 deg F tied to higher than normal humidity forecast over the region. These northern areas have lower thresholds for extreme heat compared to farther south, justifying the high risk. A moderate risk for extreme heat is posted across much of the Great Plains, Mississippi Valley, and Southeast, Jul 15-17, with heat index values potentially above 105 deg F across the Central and Southern Plains, and along the Gulf Coast and Southeast. The National Blend of Models (NBM) depicts record high minimum temperatures across parts of the Southeast into Florida, indicating little overnight relief from the heat. The slight risk of extreme heat is extended farther to the east across the Great Lakes and Ohio Valley, Jul 15-19, consistent with the ECMWF, but with confidence decreased somewhat due to the GEFS depiction. Elevated chances of extreme heat are also forecast across much of the western CONUS, although there is also uncertainty as the GEFS is much faster and more aggressive, particularly into the Northwest, and both the GEFS and ECMWF begin to weaken the ridge amplitude by the second half of the period. There is a decent signal in the uncalibrated 0z GEFS and ECMWF ensembles for temperatures above 100 deg F across low elevation areas of the Great Basin and Rockies, and possibly above 105 deg F across the California Central Valley supporting a moderate risk for extreme heat, Jul 15-17. The GEFS is more progressive at potentially pushing extreme heat farther into the Pacific Northwest, although the ECMWF is generally cooler, although the slight risk was extended into the Willamette Valley of Oregon where there are some weak signals for temperatures exceeding 90 deg F. The Desert Southwest is also downgraded to a slight risk due to the potential for monsoon moisture to lower temperatures. High temperatures over the Southwest is likely to induce thermal surface low pressure which combined with the ridge axis becoming positioned near the Four Corners, should pull tropical moisture northward into the region, kicking off the Southwest monsoon season. Dynamical models depict the potential initiation of monsoon convection as week-2 gets underway. The ECMWF and GEFS PETs depict 20 to 40 percent chances for rainfall exceeding the 85th climatological percentile and one-half inch. A slight risk of heavy precipitation is posted for much of the across portions of the Central and Southern Rockies and Desert Southwest, Jul 15-19, consistent with the PETs, and the uncalibrated ECMWF and GEFS which depict enhanced precipitation extending northward into Utah and Colorado. The signal is somewhat weaker over toward the end of week-2, tied to slow weakening of the mid-level ridge. In addition to the heavy rain threat, monsoonal thunderstorms can also produce dry lightning, resulting in increased wildfire risk. FORECASTER: Thomas Collow $$