861 FXUS21 KWNC 031759 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT May 03 2026 SYNOPSIS: Mid-level high pressure is forecast across the western contiguous U.S. (CONUS) leading to above-normal temperatures and extreme heat concerns emerging across portions of the Southwest into the California Central Valley. Conversely, persistent mid-level low pressure across the Great Lakes and Northeast favors anomalously cool weather across the region, especially early in the period. There remains the potential for late season frosts over the more northern and higher elevation areas. A frontal system ahead of the mid-level low may bring enhanced precipitation across the Gulf Coast extending into the eastern U.S. HAZARDS Moderate risk of extreme heat across portions of the Desert Southwest and the southern California Central Valley, Mon-Wed, May 11-13. Slight risk of extreme heat across portions of the southwestern CONUS and the California Central Valley, Mon-Fri, May 11-15. Slight risk of extreme heat across central and southern Florida, Mon-Tue, May 11-12. Slight risk of much below normal temperatures across portions of the Great Lakes, Ohio Valley, Appalachians, and Northeast, Mon-Tue, May 11-12. Slight risk of heavy precipitation extending from the northern Gulf Coast states through the Mid-Atlantic and Northeast, Mon-Wed, May 11-13. DETAILED SUMMARY FOR WEDNESDAY MAY 06 - SUNDAY MAY 10: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR MONDAY MAY 11 - SUNDAY MAY 17: The 0z ECMWF, GEFS, and Canadian ensembles depict a strong mid-level ridge (+120 meter positive height anomaly) over the western CONUS at the outset of the week-2 period. This feature leads to anomalously warm temperatures over much of the West and, while still early in the season, an increased chance for extreme heat over the Southwest. The National Blend of Models (NBM) and uncalibrated dynamical models depict the potential for record daily high temperatures, possibly above 100 deg F across the Desert Southwest into the southern California Central Valley. The ECMWF Probabilistic Extremes Tool (PET) depicts high probabilities (greater than 60 percent) for maximum temperatures to exceed the 90th climatological percentile over these areas, and skill weighted calibrated heat risk guidance also indicates elevated probabilities for heat to exceed the 90th climatological percentile. Therefore, a moderate risk for extreme heat is posted across the Desert Southwest into the southern California Central Valley, May 11-13. A slight risk for extreme heat extends farther north through the remainder of the California Central Valley and into southern Nevada, and is valid through May 15. The 0z ECMWF ensemble depicts some potential for temperatures near or above 90 deg F across low elevation valley areas of the Great Basin during week-2. However, the GEFS is generally cooler, and the heat risk is therefore focused on where the strongest and more consistent heat signals are over the Southwest. During the middle and later part of week-2, some of this heat may spread into the Central and Southern High Plains as the mid-level ridge slowly shifts eastward. However, the magnitude of the heat is more uncertain as the ridge is forecast to weaken compared to earlier in the period. There are weak signals for temperatures to reach the low to mid 90s deg F across the region and trends will continue to be monitored for possible heat risk addition in future updates. A persistent trough linked to the negative phase of the North Atlantic Oscillation (-NAO) remains forecast across the Great Lakes and Northeast into week-2. This continues to favor below-normal temperatures across the region. Despite it getting later into May, the ECMWF and GEFS PETs depict parts of the Ohio Valley, Great Lakes, Appalachians, and Northeast having at least a 20 percent chance minimum temperatures fall below the 15th climatological percentile and 40 deg F early in week-2. Late season frosts still cannot be ruled out across more northern and higher elevation areas, and the slight risk for much below normal temperatures remains in place, May 11-12. This same trough also favors a front to extend through the eastern U.S. and along the Gulf Coast. The 0z GEFS and ECMWF both depict enhanced precipitation along this boundary, with a more convective element possible across the Southeast and Lower Mississippi Valley before transitioning to a mid-latitude frontal wave as moisture is pulled northward into the Northeast. The GEFS is a bit faster with the progression of this feature compared to the ECMWF, but both models indicate a broad swath of 0.75 to 1.5 inches of precipitation across the East in association with this system justifying a slight risk of heavy precipitation from the Lower Mississippi Valley and Southeast, extending northward through the Mid-Atlantic and Northeast, May 11-13. South of the aforementioned frontal boundary, enhanced subtropical ridging continues to support a slight risk of extreme heat across central and southern Florida, May 11-12. The GEFS and ECMWF PETs depict at least a 20 percent chance maximum temperatures exceed the 85th climatological percentile and 90 deg F. Antecedent dry conditions may also help push temperatures upward further justifying the increased risk. Dynamical models generally indicate heat signals decreasing across the region around the middle of week-2. Over the Alaska region, models indicate possible surface low formation over the northwestern Gulf of Alaska which could bring unsettled weather to southern portions of the state. However, the strongest signals tied to this feature are during the late week-1 period, and no related hazards are posted in today's week-2 outlook. Residual troughing favors generally near- to slightly below-normal temperatures over most of the state. The typical peak of the river ice breakup season is approaching, and ice jam flooding can occur this time of year with little or no notice as conditions on frozen rivers can change quickly. Please check with the Alaska Pacific River Forecast Center for the latest conditions and advisories. FORECASTER: Thomas Collow $$