684 FXUS21 KWNC 181827 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT May 18 2026 SYNOPSIS: A continuation of mid-level cyclonic flow over the southwestern contiguous U.S. (CONUS) as well as enhanced low-level moist, southerly flow from the Gulf of America from week-1 into early week-2, supports a lingering risk for heavy precipitation mainly over the Southern Plains and Lower Mississippi Valley. The duration of above-normal precipitation coupled with the multiple rounds of potentially heavy rainfall may lead to flooding over portions of eastern Texas. Mid-level high pressure favored over southern Canada is expected to bring well above-normal temperatures for the north-central CONUS, though actual temperatures are expected to remain below heat thresholds. HAZARDS Moderate risk of heavy precipitation for the Southern Plains and Lower Mississippi Valley, Tue-Wed, May 26-27. Slight risk of heavy precipitation for portions of the Central and Southern Plains, Lower and Middle Mississippi, Tennessee, and Ohio Valleys, and Southeast., Tue-Fri, May 26-29. Flooding possible for much of eastern and central Texas, and western Louisiana. DETAILED SUMMARY FOR THURSDAY MAY 21 - MONDAY MAY 25: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR TUESDAY MAY 26 - MONDAY JUNE 01: Dynamical model 500-hPa height forecasts from the GEFS and ECMWF ensembles continue to feature anomalous ridging over the northern Pacific and southeastern Canada, with a broad coverage of positive height anomalies favored mainly east of the Rockies. While both models show weaknesses in the height pattern with broad cyclonic flow from the Desert Southwest into the Southern Plains, the GEFS and ECMWF remain at odds with evolution of troughing over the Gulf of Alaska by early next week. The GEFS favors more anomalous ridging over the northwestern CONUS, whereas the ECMWF features more amplified troughing encroaching the Pacific Northwest to bring more unsettled weather across portions of the western CONUS. As a result, there are disparities in the ensemble guidance in regards to enhanced moisture from the Pacific as well as any additional shortwave energy ejecting from the West later next week. Regardless of these differences, the pattern continues to support the potential for a lingering heavy precipitation risk associated with continued enhanced return flow from the Gulf, as well as unseasonably warm late spring temperatures over parts of the Midwest underneath the anomalous ridging favored aloft. With the continued moist, southerly flow from the Gulf favored to persist from week-1 and into early week-2, along with lingering frontal activity, a moderate risk of heavy precipitation remains posted for portions of the Southern Plains and Lower Mississippi Valley. Within the highlighted area, the uncalibrated GEFS and ECMWF tools feature at least 40% (20%) chances for 3-day amounts exceeding one (two) inch(es), with the calibrated Probabilistic Extreme Tools (PETs) also indicating at least 30% chances for amounts exceeding the 85th percentile. The moderate risk area is adjusted to cover more areas of central Texas in the updated outlook based on increased precipitation signals in the tools over this part of the state compared to yesterday. Surrounding this moderate risk area, a slight risk of heavy precipitation remains posted from the Southern and Central Plains eastward to portions of the Ohio and Tennessee Valleys and Southeast, where both GEFS and ECMWF PETs show at least 20% chances for amounts exceeding the 85th percentile and 1 inch through the middle of week-2 (May 29). The ECMWF favors a wetter solution for the lower eastern Seaboard, however this is less supported by the GEFS and is not included in the slight risk area at this time. Given the prevailing drought conditions for many areas across the South, the favored enhanced rainfall may prove to be beneficial. However, the lengthening duration of above-normal precipitation coupled with the multiple rounds of potentially heavy rainfall may trigger flooding over eastern Texas and western Louisiana, as some watersheds are already beginning to rise in response to the large influx of surface water. Days 6 and 7 QPF forecasts from the Weather Prediction Center depict precipitation totals exceeding 1-2 inches across southeastern Texas, and any continued heavy precipitation into week-2 supports the potential of river flooding. A flooding possible hazard is posted, highlighting the highest potential for river and stream flooding. However, urban and flash flooding is possible outside this area, and caution should always be exercised when approaching floodwaters. Tied to the amplified ridging over southern Canada, experimental Heat Risk tools favor the greatest chances for temperatures exceeding red level criteria over the Ohio Valley and Great Lakes early in week-2. However, both raw and calibrated temperature tools are less supportive of this risk over this part of the country, and instead favor a larger and stronger coverage of positive temperature departures focused over the north-central CONUS in proximity to the ridge center aloft during the period. A slight risk of excessive heat was considered for addition over parts of the Northern Plains and Upper Mississippi Valley, though actual temperatures look to struggle to reach into the 90s (deg F), precluding any extreme heat hazards at this time. In addition, the combination of above-normal temperatures, along with antecedent dryness may support the potential for Rapid Onset Drought (ROD) over the Northern Plains. Based on a number of precipitation forecasts which tilt slightly above-normal during week-2, there is not enough confidence to post any ROD hazards at this time, but portions of eastern Montana, North Dakota and adjacent Minnesota will be closely monitored many of these areas have received less than an inch of precipitation over the past 30 days. The stronger mean mid-level trough that is favored to shift eastward from the northeastern Pacific in the ECMWF ensemble supports the potential for high winds across portions of the West Coast, as well as across parts of the Interior West and High Plains associated with additional shortwave energy and surface low development in the lee of the Rockies. While this potential is reflected in both raw and calibrated wind tools from the ECMWF, the ridging favored in the GEFS results in lowered wind risk, and no corresponding wind hazards are issued for week-2. In Alaska, river ice breakup season is now well underway. Parts of the middle or lower Yukon are currently partially open, but are expected to be clear by the week-2 period. However, the threat of ice jam flooding would most likely be along rivers north of the Arctic Circle as they are currently mostly ice. River breakup flooding can occur with little or no notice as conditions on frozen rivers can change quickly, so please check with the Alaska Pacific River Forecast Center for the latest conditions and advisories. FORECASTER: Nick Novella $$