433 FXUS21 KWNC 061809 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT July 06 2026 SYNOPSIS: Amplified mid-level high pressure drifting into the Four Corners Region brings the risk of extreme heat to much of the western, central, and southeastern Contiguous U.S. (CONUS) through most of week-2. This pattern is expected to enhance the monsoonal circulation, potentially bringing tropical moisture and a risk of heavy precipitation into parts of the southwestern CONUS. HAZARDS Moderate risk of extreme heat for much of the Great Basin, Desert Southwest, California Central Valley, Great Plains, Mississippi Valley, Gulf Coast, Georgia, and the Carolinas, Tue-Fri, Jul 14-17. Slight risk of extreme heat for much of the western and central CONUS as well as the Gulf Coast, Southeast, Tennessee Valley, and the southern Mid-Atlantic, Tue-Sun, Jul 14-19. Slight risk of heavy precipitation for the Southern Rockies and portions of the Desert Southwest, Tue-Fri, Jul 14-17. DETAILED SUMMARY FOR THURSDAY JULY 09 - MONDAY JULY 13: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR TUESDAY JULY 14 - MONDAY JULY 20: Multiple model ensembles depict anomalous mid-level ridging building into the Four Corners Region early in week-2, with 500-hPa heights reaching a maximum of 596-dm during the early and middle part of the period, after which slight deamplification is possible. Meanwhile, a mid-level trough with near normal 500-hPa heights is forecast to settle into the northeastern CONUS. This pattern favors above-normal temperatures across most of the CONUS, and since the timing is near the height of summer, a widespread risk of extreme heat is posted across a large part of the CONUS. Only parts of the Far West, central and eastern Great Lakes, Northeast, and northern Mid-Atlantic are excluded, consistent with ensemble model means and internal heat index guidance. Southerly flow from the Gulf of America and the upper tropics is expected to prevail across the central and eastern CONUS, increasing dewpoints that would exacerbate conditions by pushing heat index values to hazardous levels. The uncalibrated extreme heat tool shows much of the CONUS with 50% or greater chances of either maximum temperature or heat index to exceed the 90th percentile at some point during week-2, as well as heat wave onset near the beginning of week-2 and lasting at least 3 to 5 days. A moderate risk of extreme heat is posted where ensemble means, dynamical models, and internal heat risk guidance show the best chances for hazardous temperatures and/or heat index values, specifically the California Valleys, lower elevations of the interior West, the Plains, the Mississippi Valley, the Gulf Coast, and portions of the South Atlantic States for Jul 14-17. A slight risk of extreme heat is also posted for an area extending farther north and east into the western Great Lakes, parts of the Tennessee and Ohio Valleys, and most of the South Atlantic States until late week-2 (Jul 19). Toward the end of the period, the European ensemble (ECENS) mean and GEFS mean show a slow deamplification of the strong mid-level ridge, reducing the extreme heat threat, but it should be noted that the typical increase in model spread at later forecast time frames may be at least partially responsible for the deamplification trend in the ensemble means. Intense heat over the Southwest is likely to induce a thermal surface thermal low pressure which 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 Probabilistic Extremes Tools (PETs) from the ECENS, GEFS, and Canadian ensembles (CMCE) are a little more robust and consistent with this development today, with 20 to 40 percent chances for rainfall above the 85th climatological percentile and exceeding one-half inch shown for much of the region during the first half of week-2. A slight risk of heavy precipitation is posted for much of the Southwest, consistent with the guidance. The signal is somewhat weaker over the last half of week-2, at least partly in concert with the possible slow deamplification of the strong mid-level ridge. In addition to the heavy rain threat, monsoonal thunderstorms can also produce dry lightning, resulting in increased wildfire risk. FORECASTER: Rich Tinker $$