522 FXUS21 KWNC 211809 PMDTHR US Hazards Outlook NWS Climate Prediction Center College Park MD 300 PM EDT April 21 2026 SYNOPSIS: A slow-moving frontal boundary is forecast to interact with moist southerly flow early week-2, increasing the potential of heavy precipitation for portions of the Southern Plains, the Tennessee and Lower Mississippi Valleys, and the Southeast. Surface low pressure development is possible over or near the eastern contiguous United States (CONUS) toward the middle of the period with another frontal boundary possibly affecting parts of the South late week-2, but there is too much uncertainty to post any associated hazards at this time. HAZARDS Slight risk of heavy precipitation for portions of the Southern Plains; the Tennessee, Lower Mississippi, and southern Ohio Valleys; and adjacent areas of the Southeast and southern Appalachians, Wed-Thu, Apr 29-30. DETAILED SUMMARY FOR FRIDAY APRIL 24 - TUESDAY APRIL 28: https://www.wpc.ncep.noaa.gov/threats/threats.php FOR WEDNESDAY APRIL 29 - TUESDAY MAY 05: Ensemble solutions from the ECENS and GEFS for 500-hPa height anomalies depict a shortwave trough moving from the western Contiguous U.S. (CONUS) to the Great Lakes by the outset of the week-2 period, with an accompanying surface low pressure and a trailing cold front ahead of the trough. Models favor this frontal boundary to move slowly through the South from the southeastern Great Plains through the lower Mississippi and Tennessee Valleys, into the Southeast. These features are not particularly amplified but form while moderate southerly flow is established to the west of a surface high pressure system over the western North Atlantic. This return flow is anticipated to increase moisture available to the developing system, enhancing precipitation accumulations. The Probabilistic Extremes Tool (PET) from the European ensemble (ECENS) shows 30 to 40 percent probabilities of 3-day precipitation accumulations exceeding 1 early week-2 over much of the lower Mississippi Valley and some adjacent areas. PETs from the GEFS and the Canadian ensemble (CMCE) are less robust, showing 20 to 30 percent chances for 3-day totals over an inch. The ECENS mean depicts 1 to 2 inches of rain from central Mississippi eastward into Georgia and northeastward into Kentucky while the dynamical European model (ECMWF) shows a less widespread pattern of heavy rain, but with localized areas approaching 3 inches. These factors support a slight risk of heavy precipitation from portions of the Southern Plains through the Lower Mississippi and Tennessee Valleys and into adjacent sections of the Ohio Valley, Southeast, and southern Appalachians Apr 29-30. By May 1, the cold front is expected to have cleared the Gulf and South Atlantic coasts, ending the heavy rain threat. Isolated, brief high wind gusts are possible associated with potentially strong thunderstorms, but guidance does not support widespread strong winds, so no high wind threat is posted. As the cold front clears the southern and eastern CONUS, some models show a surface low pressure system forming somewhere over or near the eastern CONUS that gets picked up by the negatively-tilted mid-level trough moving toward the Great Lakes and New England. The dynamical ECMWF artificial intelligence model (ECMWF-AI) is most robust with such a system, showing low pressure forming over the South Atlantic region and moving up the Eastern Seaboard. If a significant surface storm system develops, heavy precipitation could affect all or part of the Great Lakes and Atlantic Seaboard, particularly in the northeastern CONUS which will be downstream from a mid-level trough. At this time, there is too much uncertainty to justify posting any hazards, but the situation will continue to be monitored. Breezy conditions are likely in the wake of the cold front as cool and dry high pressure settles into the central and eastern CONUS. Winds are not expected to reach hazards thresholds, but large portions of this region are currently entrenched in some degree of drought. The combination of dry and breezy conditions over parts of the central and eastern CONUS where there is antecedent dryness significantly increases the risk of wildfire activity, which could spread rapidly. Care should be taken to minimize the chances of wildfire initiation. Later in week-2, some tools, including the ECMWF, show another cold front moving into the South, potentially triggering another round of heavy precipitation there. At this time, most tools favor sub-hazardous precipitation totals with this system, and some models do not show any late-week frontal system affecting this region. This, along with run-to-run inconsistency among the models, precludes posting any related hazards at this time. No hazards are issued over Alaska, with nondescript weather expected under slowly-building mid-level heights. However, 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. Check with the Alaska Pacific River Forecast Center for the latest conditions and advisories. FORECASTER: Rich Tinker $$