FXUS21 KWNC 091821 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT July 09 2026 SYNOPSIS: Highly amplified mid-level high pressure is forecast to peak in amplitude across the north-central contiguous U.S. (CONUS) during week-1. Dynamical model ensembles have trended more east with this feature, and now support increasing extreme heat risks from the Northern Plains to the Midwest and Eastern Seaboard at the outset of week-2 coinciding with the peak of summer time heating. There is a bit less confidence across the West compared to previous outlooks, where above-normal temperatures are likely, but the decreasing amplitude of mid-level high pressure reduces the chances of extreme heat. 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, Fri, Jul 17. Moderate risk of extreme heat across the Northern and Central Plains, Upper and Middle Mississippi Valley, lower Great Lakes, and the Tennessee and Ohio Valleys, Fri-Sat, Jul 17-18. Moderate risk of extreme heat across portions of the southern Mid-Atlantic and Southeast, Fri-Sat, Jul 17-18. Slight risk of extreme heat for most areas from the Great Plains to the East Coast, Fri-Mon, Jul 17-20. Slight risk of extreme heat across much of the western CONUS, Fri-Thu, Jul 17-23. Slight risk of heavy precipitation across portions of the Central and Southern Rockies and Desert Southwest, Fri-Tue, Jul 17-21. Rapid Onset Drought risk across the Northern Plains. DETAILED SUMMARY FOR SUNDAY JULY 12 - THURSDAY JULY 16: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR FRIDAY JULY 17 - THURSDAY JULY 23: A broad mid-level ridge is forecast across most of the CONUS at the outset of week-2, with the ECMWF ensemble depicting a 595-dm 500-hPa center across the Lower Mississippi and Tennessee Valleys. As a result, +60 meter positive height anomalies extend across the Midwest and Ohio Valley, with +30 meter positive height anomalies reaching the East Coast on day-8 (Jul 17). While the ECMWF has always been on the eastern edge of the guidance in terms of ridge placement, this is a substantial shift compared to yesterday, and the GEFS has also trended in this direction. Additionally, both the deterministic 0z GFS and ECMWF depict the most amplified ridging over the eastern U.S. early in week-2. The forecast leans more on the ECMWF due to recent model skill in persisting the previous heat wave across the eastern U.S., and therefore, risks of extreme heat are now being highlighted from the Northern Plains eastward across the Ohio Valley and to the East Coast. A high risk for extreme heat remains posted for Jul 17 across the Northern Plains and adjacent areas of the Upper Mississippi Valley 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. The moderate risk for extreme heat is expanded across the Midwest and Ohio Valley, valid Jul 17-18, and consistent with 40 percent or greater probabilities of maximum temperatures exceeding the 85th climatological percentile in the ECMWF Probabilistic Extremes Tool (PET). The 0z ECMWF ensemble continues to depict maximum temperatures in the upper 80s to low 90s deg F, and with a notable upward trend in temperatures compared to yesterday in the GEFS. Higher heat index values are likely farther south, potentially exceeding 105 deg F across the Middle Mississippi Valley. Hot temperatures and predicted dry conditions also support an enhanced risk of Rapid Onset Drought across portions of the Northern Plains. There are also stronger signals for extreme heat across the Eastern Seaboard, with a moderate risk for extreme heat across the southern Mid-Atlantic into the Southeast, Jul 17-18. This is mainly tied to elevated probabilities for heat index values to exceed the 90th climatological percentile in the GEFS/ECMWF skill weighted heat risk guidance, and also supported by enhanced subtropical ridging and above-normal sea surface temperatures over the northeastern Gulf of America. The uncalibrated 0z ECMWF supports a farther northward expansion of the moderate risk through the northern Mid-Atlantic where there are emerging chances of temperatures exceeding 100 deg F. However, there is still some uncertainty tied to the amplitude of troughing over Atlantic Canada, with the GEFS favoring lower mid-level heights compared to the ECMWF. A broad slight risk for extreme heat covers most areas from the Great Plains to the East Coast, Jul 17-20, with enough support, especially in the ECMWF, to justify expanding the slight risk for extreme heat through southern New England, with the greatest potential being earlier in the period. The National Blend of Models (NBM) indicates the potential for both record high maximum and high minimum temperatures across parts of the eastern Coastal Plain, suggesting little overnight relief from the heat. Elevated chances of extreme heat are also forecast across much of the western CONUS, although there is also uncertainty as the GEFS is quicker to shift the ridge west, and both the GEFS and ECMWF begin to weaken the ridge amplitude by the middle 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 slight risk for extreme heat for all of week-2. Probabilities in the PETs are on the lower side and no longer support a moderate risk. High temperatures over the Southwest are 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. The ECMWF PET depicts 40-60 percent chances for rainfall exceeding the 85th climatological percentile and one-half inch early in the period, decreasing later in week-2. Probabilities in the GEFS PET are generally low, but still indicate an enhanced signal (at least 20 percent chance) through the middle of the period. Therefore, a slight risk of heavy precipitation is posted for much of the Central and Southern Rockies and Desert Southwest, Jul 17-21, 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 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 $$