290 FXUS21 KWNC 101818 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT July 10 2026 SYNOPSIS: Deamplifying mid-level high pressure is favored throughout much of the contiguous U.S. (CONUS) resulting in a lowered risk of extreme heat conditions during week-2. The greatest risk of extreme heat looks to be focused over parts of the northwestern and northcentral CONUS in proximity to the anomalous mid-level high pressure forecast. Downstream, more mid-level low pressure is favored early in week-2, which is expected to bring cooler temperatures and allay heat concerns for many areas east of the Mississippi. However, surface low development over the Southeast increases the risk of heavy precipitation, as well as favored enhanced subtropical ridging to promote a lingering heat risk for the eastern Gulf of America states. This prevailing mid-level pattern is also consistent with an enhanced monsoonal circulation, potentially bringing tropical moisture and a risk of heavy precipitation into parts of the southwestern CONUS. HAZARDS Moderate risk of extreme heat across the Northern and Central Plains, adjacent parts of the Mississippi Valley, Rockies and Northern Great Basin, Sat-Sun, Jul 18-19. Moderate risk of extreme heat across portions of the Florida Peninsula Sat-Sun, Jul 18-19. Slight risk of extreme heat across parts of California, Pacific Northwest, Great Basin, Rockies, Northern and Central Plains, Middle and Upper Mississippi Valley, Sat-Wed, Jul 18-22. Slight risk of extreme heat for coastal portions of the Lower Mississippi Valley and Southeast Sat-Fri, Jul 18-24. Slight risk of heavy precipitation for the lower Eastern Seaboard, Sat-Mon, Jul 18-20. Slight risk of heavy precipitation for much of the Four Corners, Sat-Wed, Jul 18-22. Rapid Onset Drought risk across the Northern Plains. DETAILED SUMMARY FOR MONDAY JULY 13 - FRIDAY JULY 17: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR SATURDAY JULY 18 - FRIDAY JULY 24: Late in week-1, dynamical model 500-hPa height anomaly forecasts from the GEFS and ECMWF ensembles remain in good agreement featuring anomalous mid-level ridging overspreading much of the CONUS. A highly amplified mid-level height anomaly center continues to be favored over the north-central CONUS, along with a secondary ridge center extending eastward into the Mid-Atlantic and the Southeast, both of which are expected to promote elevated risks of extreme heat coinciding with the climatological peak of summertime heating. By the outset of week-2 (Jul 18), there is increased model support for the eastward extension of this 500-hPa ridge to deamplify in the models, with the latest 0z ECMWF ensemble featuring a fairly swift transition towards developing a mean trough, with negative height departures centered over the eastern U.S. on day 9. The depth of the mean trough axis has become increasingly pronounced compared to previous ECMWF ensemble guidance over the past few days. By comparison, the 0z GEFS is slower with this transition, but nonetheless favors lowering heights and more northwesterly flow to mitigate a lingering extreme heat risk with cooler temperatures. Concurrent with the deamplifying ridging over the eastern U.S. early in the period, much of the mid-level ridging upstream is also favored to weaken, though positive height departures remain favored to sustain an increased heat risk over many parts of the western CONUS at least through the middle of the period. Based on the deamplifying pattern, with more troughing and cooler temperatures favored over the eastern U.S. early in the period, the high risk extreme heat is discontinued over the Northern Plains and Upper Mississippi Valley in the updated outlook, as the hottest temperatures look to time off during week-1. However, a moderate risk (40-60% chance) of extreme heat remains issued over the Northern and Central Plains (Jul 18-19), with its coverage expanded to include more of the Interior West and western portions of the High Plains in proximity to the anomalous ridge center. The moderate risk coverage is removed over the Mississippi, Tennessee and Ohio Valleys, and Great Lakes due to cooler temperatures favored in the raw and calibrated tools over this part of the country. Within the moderate risk area, there remains increased chances for heat index values exceeding 100 (105) deg F in the Northern (Central) Plains, with the uncalibrated ECMWF and GEFS showing elevated chances (>30%) for double digit positive temperature departures, and the GEFS Probabilistic Extremes Tool (PET) indicating similar chances for daytime temperatures exceeding the 85th climatological percentile for the first few days of period. Despite a small tilt towards near to above-normal precipitation favored for the Dakotas during week-2, the combination of anomalous warmth and antecedent dryness supports an enhanced risk of Rapid Onset Drought across portions of the Northern Plains. Surrounding the moderate risk area, a slight risk of extreme heat remains is posted for much of the western CONUS, excluding the parts of the lower Four Corners where temperatures tools indicate cooler temperatures associated with an uptick in monsoonal precipitation (discussed below). There continues to be decent signals 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 the slight risk area. The slight risk remains valid through Jul 22, as models favor more of a zonal pattern developing over the CONUS late in week-2, with weakly positive mid-level height departures limited to the higher latitudes in Canada. Even with cooler temperatures favored over the eastern U.S. enhanced subtropical ridging and accompanying heat risks still remains a concern over the Gulf States. Both PETs maintain at least 20% chances of maximum temperatures exceeding the 85th percentile over parts of Lower Mississippi Valley and the Southeast, with the ECMWF PET favoring higher chances (>40%) for exceeding this threshold concentrated over the Florida Peninsula. In addition, sea surface temperatures in the eastern Gulf continue to run very warm, with anomalies registering upwards of 2 degrees C to support continued surface warmth. Therefore, a slight risk of extreme heat is posted along the coast from Louisiana to Florida for Jul 18-24, with an embedded moderate risk area (Jul 18-19) over parts of central and southern Florida where the National Blend of Models (NBM) highlights several locations with warm highs and lows nearing or breaking daily records early in the period. Tied to more troughing favored over the eastern U.S., there is increased ensemble support for surface low development to the north of the subtropical ridge over parts of the Southeast and the Mid-Atlantic. While the GEFS PET remains rather muted with a heavy precipitation risk, the ECMWF PET now favors increased chances for 3-day amounts exceeding the 85th percentile and 1 inch, with the uncalibrated GEFS and ECMWF showing a significant increase in the exceedance probabilities relative to yesterday. Therefore, a slight risk of heavy precipitation is posted over much of the lower Eastern Seaboard for Jul 18-20. Based on the PETs, elevated wind speeds are also possible within the slight precipitation risk area, though there remains a fair amount of ensemble spread in regards to strength and position of the low to induce hazardous winds onshore, thus no corresponding wind hazard is posted. Triple-digit daytime temperatures over the Sonoran Desert are likely to induce thermal surface low pressure, which combined with the ridge axis positioned near the Four Corners, is expected to advect tropical moisture northward into the region, kicking off the Southwest monsoon season. In addition, the National Hurricane Center (NHC) is currently monitoring multiple areas for Tropical Cyclone (TC) development in the central and eastern Pacific, with one area closer to Mexico with 70% chances for formation during the next seven days. Should formation occur next week, a potential track nearing the Gulf of California could initiate a Gulf Surge and bring additional moisture and precipitation into the Southwest. There continues to be good support in the GEFS and ECMWF PETs indicating 20-40% chances for 3-day accumulated amounts exceeding the 85th percentile, and a slight risk of heavy precipitation remains posted for much of the Four Corners (Jul 18-22). The favored uptick in monsoonal activity is likely to keep an excessive heat risk at bay during the period, however, monsoonal thunderstorms can also produce dry lightning, resulting in increased wildfire risk. Given the stronger signals for above-normal temperatures further north, there is also an increased risk of wildfires across the Interior West and High Plains as well. FORECASTER: Nick Novella $$