Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Mon Apr 13 2026 Valid 131300Z - 141200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN MINNESOTA AND PARTS OF WISCONSIN... ...SUMMARY... Severe thunderstorms are likely across the Upper Mississippi Valley and Great Lakes region with potential for large to very large hail, damaging wind, and tornadoes, mainly late this afternoon into tonight. A more conditional and isolated risk for severe storms is possible across portions of the southern Plains late this afternoon and evening. ...Upper Mississippi Valley/Great Lakes including MN/WI... Multiple lead mid-level disturbances over the northern High Plains will progress northeastward today toward the Upper Midwest, with strengthening winds aloft across this region particularly late today and tonight. A surface low will tend to deepen/develop east-northeastward from northeast Nebraska this morning into far southern Minnesota and Wisconsin by tonight in vicinity of a slow-moving/stalled frontal boundary. Low/middle 60s F surface dewpoints will advect north-northeastward and become increasingly prevalent along/south of the aforementioned stationary/warm front this afternoon. MLCAPE values are forecast to reach 2000-2500 J/kg by around 21z/4pm CDT. Thunderstorm development will become increasingly probable through mid/late afternoon (21-00z) as isentropic ascent strengthens ahead of the approaching upper disturbance. Lingering inhibition coupled with 45-50 kt effective bulk shear should promote initially discrete supercells along or just north of the surface boundary. Hodograph elongation appears favorable for a large hail threat, possibly as large as 2-3 inches in diameter with the more robust cells. Additionally, enhanced low-level SRH along the frontal zone is expected to result in a corridor of relatively higher tornado potential for storms that can remain rooted immediately along the boundary. While the overall environment appears very favorable for intense convection/supercells, east-northeasterly storm motions along or just north of the warm front will likely promote clustering/upscale growth through the evening, with an increasing damaging wind potential and a continued tornado risk via line-embedded circulation potential. ...Northern Illinois/northern Indiana and southern Lake Michigan... There is the potential that a somewhat separate corridor of severe-weather potential may unfold today, potentially born out of subtle mid-level wave and early morning convection across northeast Missouri vicinity and/or development later today. The initially elevated storms would be on the edge of the east/northeastward-advecting elevated mixed layer. Steep mid-level lapse rates and 35+ kt effective shear could support initially isolated hail potential, but a more organized surface-based severe risk could manifest if some of the more-aggressive early morning short-term guidance trends materialize (HRRR/RAP/RRFS). ...Southern Plains including Oklahoma/Texas... A moist and potentially unstable air mass will persist regionally to the east of a dryline located around peak heating from east-central Kansas south-southwestward into west-central Oklahoma and western north Texas to the Texas Big Bend vicinity. Immediately east of the dryline, warm-sector dewpoints are expected to generally be in the middle 60s F, supporting MLCAPE values to 2500-3000 J/kg. The extent/likelihood of sustained deep convection later today is a key question. The primary southern-stream trough will be well upstream over the southwest Desert, with neutral height tendencies across the southern Plains, although early morning water vapor imagery and derived wind data suggest that a subtle disturbance over northern Mexico and the southern Rockies could approach the dryline/warm sector later today. Regardless, ample post-dryline mixing and near-dryline confluence/weak convergence may be sufficient for deep convective initiation after 21z/4pm CDT, at least an isolated basis. Forecast mass fields would imply that this is most probable across central/southwest Oklahoma into the north Texas Big Country, and perhaps somewhat separately across the Texas Big Bend and Rio Grande vicinity. If/where storms develop and mature, deep-layer shear on the order of 40+ kt will support supercells, potentially capable of all hazards including very large hail. An increased confidence in deep convective initiation late this afternoon/early evening could warrant focus Slight Risk delineations in subsequent Day 1 updates. ...Northern High Plains... Generally isolated severe storms capable of hail/wind will be possible late this afternoon into evening along/north of the surface front where modest low-level moisture and vertical shear will be maximized, in the presence of steep low/mid-level lapse rates. ..Guyer/Broyles.. 04/13/2026Read more