219 ACUS01 KWNS 182006 SWODY1 SPC AC 182005 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0305 PM CDT Mon May 18 2026 Valid 182000Z - 191200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF CENTRAL AND NORTHEASTERN KANSAS...FAR SOUTHEASTERN NEBRASKA...NORTHWESTERN MISSOURI...AND FAR SOUTHWESTERN IOWA.... ...SUMMARY... Numerous severe thunderstorms are expected this afternoon and evening across the south-central Plains and mid Missouri Valley. Supercells capable of producing very large to giant hail and multiple strong to intense tornadoes remain likely from central Kansas and southeast Nebraska into Iowa and northwest Missouri. ...20z Update Midwest Lower Great Lakes... An expansive MCS remains ongoing over portions of the lower Great Lakes this afternoon. The environment ahead of the complex is unstable, but with gradually decreasing moisture/buoyancy farther east. An isolated severe risk likely exists ahead of the line across OH and lower MI through this evening. A large cold pool behind the complex has overturned the air mass across much of northern IL, southern WI and eastern IA. This should greatly limit air mass recovery this afternoon and evening. Additional convection originating from the central Plains and mid MO valley may continue eastward, but is forecasted to weaken as it encounters the cooler air mass tonight. Isolated storms, likely elevated, could persist with a risk for hail, but the severe potential has decreased such that, probabilities were lowered. ...Central Plains and Mid MO Valley... Several supercells and organized clusters have emerged across parts of KS and southern NE. A very unstable and strongly sheared environment remains in place ahead of these storms. This should support a risk for all hazards, include strong tornadoes, very large hail, and significant damaging winds. Current expectations are for the individual supercells to grow upscale into one or more clusters as they interact with a modifying outflow boundary across northeast KS and northwestern MO. While the environment becomes gradually less unstable farther north and east, very strong shear will likely support a continued risk for all hazards this evening. The western portions of the risk area has been trimmed in parts of central KS where the cold front has sagged southward. ...Southwest TX.. Strong diurnal heating along southern portions of the dryline has resulted in isolated storm development this afternoon. Very large buoyancy (MLCAPE 3000-4000 J/kg) and steep lapse rates will likely continue to support high-based isolated storms. Vertical shear is marginal, but sufficient for supercells with hail and damaging wind potential. Have extended severe probabilities southward along the dryline. ..Lyons.. 05/18/2026 .PREV DISCUSSION... /ISSUED 1125 AM CDT Mon May 18 2026/ ...Central Plains... Morning water vapor loop shows a potent shortwave trough rotating across the central Rockies into western KS. The primary surface boundary extends from western IA into central KS, with a pronounced outflow boundary associated with overnight convection extending from southeast KS into southern MO. The outflow boundary will lift northward today, allowing a very moist and extremely unstable air mass to spread into eastern KS/northwest MO/extreme southeast NE/southwest IA. This is the area most concerning for intense supercells later today. Initial storms are expected to develop by early afternoon near the triple point of the retreating outflow boundary and cold front. These storms will track northeastward through the afternoon and early evening in a strongly sheared environment favorable for tornadoes, very large hail, and damaging winds. It remains unclear how stormscale interactions will impact discrete supercell mode, but strong tornadoes are a concern in this region. Farther southwest, thunderstorms will develop in vicinity of the cold front across south-central KS by late afternoon. Recent CAM solutions suggest these storms may be affected by the linear frontal forcing, and may be slightly anafrontal. This would lessen the tornado risk, but very large hail and damaging winds would remain a concern. No changes have been made to the Moderate Risk area due to conflicting model signals. ...Western OK/Northwest TX... Full sunshine will lead to hot temperatures along the dryline over western OK into northwest TX. At least isolated thunderstorms are expected to form in this area, with a risk of large hail and damaging winds. Weak large scale forcing may limit storm duration and intensity. ...OH Valley/Great Lakes... A line of thunderstorms along the IL/IN border is tracking northeastward into a warm/moist air mass. Relatively strong low-level wind fields and steep low-level lapse rates suggest a continued risk of scattered wind damage with the strongest storms as they track across parts of IN/Lower MI/Northwest OH. $$