108 FXUS21 KWNC 171824 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT July 17 2026 SYNOPSIS: A westward shifting and strengthening area of mid-level high pressure is expected to bring an elevated risk of extreme heat over portions of the southwestern and southcentral contiguous U.S. (CONUS) through the middle of the period, with increasing chances for extreme heat and a rapid onset drought risk also favored for the northcentral CONUS. A more suppressed monsoonal circulation is expected to limit chances for heavy precipitation with drier conditions favored for the lower Four Corners. However, stalled frontal activity favored over the southeastern CONUS supports a heavy precipitation risk over the Southeast and lower Mid-Atlantic early in the period. HAZARDS Moderate risk of extreme heat for parts of the Southern and Central Plains, adjacent parts of the Lower Mississippi Valley, and Desert Southwest, Sat-Tue, Jul 25-28. Slight risk of extreme heat for the California Valley, Desert Southwest, Great Basin, Rockies, Great Plains, Lower Mississippi Valley, and Southeast, Sat-Fri, Jul 25-31. Slight risk of heavy precipitation for parts of the lower Mid-Atlantic and Southeast, Sat-Mon, Jul 25-27. Rapid onset drought (ROD) possible for portions of the Dakotas. DETAILED SUMMARY FOR MONDAY JULY 20 - FRIDAY JULY 24: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY JULY 25 - FRIDAY JULY 31: Heading into the start of week-2, dynamical models are in good agreement featuring anomalous 500-hPa ridging centered over portions of the Interior West and Great Plains, bookended by a pair of mean longwave troughs, with one over the northeastern Pacific, and the other overspreading much of eastern North America. Over time, both the GEFS and ECMWF ensembles continue to favor an amplification of the ridging over the CONUS, as well as a shift of the anomalous ridging that becomes more positively tilted towards the middle of the period. Consequently, stronger mid-level positive height departures are featured along an axis from the north-central to southwestern CONUS, with the ECMWF in particular, featuring the emergence of a mean 597-dm contour center over the lower Four Corners early in the period, translating to over 2 standard deviations above peak summer climatology. The rising 500-hPa heights favored are anticipated to bring a higher risk of extreme heat across the western and central CONUS, while keeping this risk at bay for many areas downstream east of the Mississippi where more troughing and accompanying northwesterly flow is forecast. Underneath the stronger ridging aloft, an elevated potential for heat risk continues to be supported by a number of temperature and heat tools for many parts of the southern tier of the U.S during the week-2 period. With high dewpoints remaining favored east of the Rockies to help drive high heat index values, a moderate risk of extreme heat remains posted over the Southern Plains for Jul 25-28, with coverage adjusted to include (exclude) more the Southern and Central Plains and Desert Southwest (Lower Mississippi Valley). These adjustments are mainly based on the evolving ridge pattern and the associated changes favored in the temperature anomalies and probabilities in both the raw and calibrated tools. Within the highlighted moderate risk area, there are increased chances for heat index values exceeding 110 (105) deg F across the Southern Plains and parts of the Lower Mississippi Valley (Central Plains), with daytime maximum temperatures above 110 deg F over the lower elevations of the Desert Southwest. Surrounding the moderate risk area, a slight risk of extreme heat remains posted with its coverage likewise expanded to include portions of the California Valley, Interior West, and Great Plains. Ensembles show the greatest warming trend in proximity to the strongest mid-level height anomalies in the Northern Plains (with 50-60% chances for double digit positive temperature departures) supportive of this expansion over northcentral CONUS, however heat tools show fairly low chances of heat index values exceeding the 90th climatological percentile. Although this part of the country is less likely to reach hazardous heat criteria, the combination of antecedent dryness, anomalous warmth and dryness during week-1, with near to slightly above normal precipitation favored during week-2, supports an enhanced risk of Rapid Onset Drought (ROD) across portions of the Northern Plains. The slight risk area of extreme heat also remains extended through portions of the Southeast and into the Florida Peninsula where enhanced subtropical ridging may linger and anomalously warm SSTs are registered in the Gulf to support continued anomalous warmth. Despite the stronger mid-level ridging favored over the southwestern CONUS, the mean ridge center looks to be in a less favorable position for the broad scale advection of monsoonal moisture. This is supported in both the raw and calibrated precipitation guidance which has favored a drying trend over the past day or so, with Probabilistic Extreme Tools (PETs) now indicating limited chances of 3-day precipitation amounts exceeding the 85th percentile over the lower Four Corners. Therefore, the slight risk of heavy precipitation is discontinued in the updated outlook. However, scattered thunderstorm activity across the region cannot be ruled out, and any upticks in monsoonal moisture can also produce dry lightning, resulting in increased wildfire risk where precipitation does not fall. Tied to the mid-level troughing favored over the eastern U.S., a slight risk of heavy precipitation remains posted for parts of the Southeast and lower Mid-Atlantic for Jul 25-27, with an increase in coverage over the Southeast and Florida Panhandle in the updated outlooks. Ensembles continue to point to stalled frontal activity to maintain this increased risk early in week-2. Both the PETs and uncalibrated guidance bring at least 20% chances for three day precipitation amounts to exceed the 85th climatological percentile and 1 inch, with raw tools showing increased wet signals over the Florida Panhandle and eastern Gulf relative to yesterday. FORECASTER: Nick Novella $$