SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0737 AM CDT Mon Apr 28 2025 Valid 281300Z - 291200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR SOUTHERN MN...NORTHERN IA...AND WESTERN WI... ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM NORTH-CENTRAL AND WESTERN OK INTO THE TX BIG COUNTRY AND SOUTHWEST TX... ...SUMMARY... Multiple corridors of severe thunderstorms are expected across the Upper Midwest later today into tonight, with a regional severe weather outbreak possible. The most dangerous period is likely during the late afternoon and evening when strong tornado potential should be maximized. Scattered large to very large hail and damaging winds are likely as well. ...Synopsis... Recent satellite imagery shows a mature cyclone centered over UT, with a shortwave trough progressing northeastward through the central High Plains within the eastern periphery of this cyclone. Farther north, overnight convection across SD has contributed to the development of vorticity maximum, which is currently moving into western MN. Early morning surface analysis places a deep low over central SD, with a dryline extending south-southwestward from this low across central NE, western KS, the northwest TX Panhandle, southeast NM, and far West TX. A warm front extends eastward from this low to the ND/SD/MN border vicinity before then arcing more southeastward across southwest MN, central IA, and eastern MO. A large warm sector characterized largely by 60s dewpoints exists between these two features. Expectation for the central High Plains shortwave trough to progress quickly northeastward throughout the period, accompanied by a strong jet streak (i.e. 70 to 80 kt at 500 mb). The surface low will eject northeastward as well, reaching central MN by 00Z and continuing into northwestern Ontario by 12Z Tuesday. Coincident northward/northeastward movement of the warm front will bring a warm, moist, and unstable airmass into the Upper Midwest ahead of the approaching dryline, which will likely extend from central MN southwestward into the TX Permian Basin by mid-afternoon. Severe thunderstorms are expected to develop along the length of this dryline, with the greatest severe potential across the Upper Midwest. ...Upper Midwest... A regional severe weather outbreak still appears possible across the Upper Midwest, with a threat of strong to intense tornadoes, very large hail, and swaths of damaging winds. Convective line ongoing across central MN is expected to continue quickly northeastward through the region, leaving ample time for the warm front to progress northward and bring a warm, moist, and unstable airmass into the region ahead of the dryline. Thunderstorm initiation along the dryline is forecast to begin around 18-20Z near the SD/MN/IA border intersection vicinity, before then continuing quickly eastward across southern MN and northern IA throughout the late afternoon and early evening. Volatile environmental conditions are expected south of the warm front and east of the dryline, with strong instability (MLCAPE near/above 3000 J/kg) and deep-layer shear, and a persistently intense low-level jet that will maintain very favorable low-level shear/SRH. This environment will be conditionally favorable for long-track supercells with strong/intense tornado potential if a discrete mode can be maintained. Quick upscale growth into a more linear or cluster mode is possible, but the vertical shear appears strong enough for a discrete mode to be maintained as well. A scenario where a primary line develops with discrete storms ahead of it is possible as well. In any case, the overall environment supports the potential for large to very large hail, damaging gusts, and strong to intense tornadoes with any discrete storms. Line-embedded tornadoes and strong gusts are possible within any convective lines. A more conditional scenario exists farther south from central IA into northeast KS/northwest MO. Here, the kinematic environment will remain supportive of supercells capable of all severe hazards, but capping could prove detrimental to deep convection given the weaker low-level convergence and large-scale ascent. Any supercell that can initiate and be sustained could become long-tracked within the expanding and very favorable warm sector, posing a threat for strong to intense tornadoes and very large hail. Farther west, a couple of supercells may develop in the region between the prefrontal trough/dryline and cold front, and pose a threat of large hail and locally damaging gusts as they move across northeast NE/southeast SD into parts of MN/IA. ...Western/Central OK...Northwest/Southwest TX... Daytime heating, and resultant airmass destabilization, coupled with convergence along the dryline is expected to result in convective initiation from the TX Big Country into southwest TX during the afternoon. Steep lapse rates and strong vertical shear will support supercells, with large to very large hail as the primary severe risk. Farther north in western OK, convective development will likely wait until around 00Z when the dryline begins to retreat. The increased low-level moisture coupled with a reduction in convective inhibition could result in a 2-4 hour window where convective initiation is more likely. At the same time, the low-level jet is forecast to strengthen considerably, resulting in a kinematic environment supportive of supercells. The tornado threat would likely maximize between 00-04Z before nocturnal stabilization forces storms to become more elevated. Hail potential could persist into north-central OK as any storms that develop progress northeastward throughout the night. ..Mosier/Broyles.. 04/28/2025