Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 21 2025 05:53:46 ACUS01 KWNS 210553 SWODY1 SPC AC 210552 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1252 AM CDT Mon Jul 21 2025 Valid 211200Z - 221200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF CENTRAL AND EASTERN MONTANA... ....SUMMARY... Severe thunderstorms capable of producing severe wind gusts, large hail, and perhaps a tornado or two are expected across parts of the northern Great Plains. Additional isolated strong to severe storms are possible in the central Plains. ....Synopsis... Modest amplification of an upper-level ridge is expected across the Plains into the Upper Midwest today. In the Northwest, the upper-level trough will take on a more neutral tilt before progressing eastward by Tuesday morning. At the surface, modest lee troughing will be in place within the northern/central High Plains regions. An outflow boundary is likely to be situated somewhere in the North Dakota/South Dakota border vicinity. Farther east into Minnesota, a warm front like feature will arc southeastward into the lower Ohio Valley. Strong to extreme buoyancy is forecast to develop within parts of the northern/central Plains. ....Montana into western North Dakota... The highest confidence in the development of severe storms is within the terrain of central Montana. Additional storms may develop in the vicinity of the Big Horns and move into southeast Montana. Mid-level heights will be rising through the morning/afternoon so initiation could be somewhat delayed. Subtle mid-level height falls will occur during the evening, however. With a belt of strong mid-level winds across the region, initial storms should be supercellular. Large hail and severe wind gusts will be the initial hazards. With storms developing in somewhat drier air, it is possible they will be outflow dominant and not maintain their cellular mode as they move northeast into greater moisture. The environment will be conditionally favorable for 2+ inch hail, but the spatial extent of this threat is not certain. Severe wind gusts will likely become more common later in the evening as activity grows upscale. ....Dakotas into Minnesota/Mid-Missouri Valley... Two clusters of convection are ongoing in the Dakotas. Based on current surface observations, this activity is expected to generally move eastward along the North Dakota/South Dakota border. What occurs with the outflow from this activity into this afternoon will play a role in the severe potential within parts of the Dakotas. Strong to extreme buoyancy will be present south of the outflow. Forcing for ascent will be weak. Storm development will depend on the timing of the early morning convection and subsequent heating/mesoscale lift during the afternoon. A weak surface low in western South Dakota may lead to some locally enhanced convergence along the outflow and trigger storms. This scenario is also not certain. Effective shear of 40-45 kts and MLCAPE likely above 4000 J/kg will support intense, organized storms. Initial storms would be capable large hail, severe winds, and perhaps a tornado or two. Storms that do develop would eventually grow upscale and potentially produce a swatch of severe winds. Model guidance varies on the timing/location of this activity. There is some potential for a cluster/MCS to propagate along the warm front feature into central Minnesota. Other solutions show the MCS moving into the greater buoyancy toward the Mid-Missouri Valley. Given some capping can be expected, storms may not develop at all. The marginal risk has been expanded to account for these possibilities, but confidence remains too low for a categorical upgrade at this time. ....Central High Plains... Strong heating near the surface trough should promote isolated to widely scattered storms from the Palmer Divide into the Nebraska Panhandle. Effective shear of 25-30 kts (generally weaker with southern extent) will allow for marginally organized storms. Severe wind gusts are the main concern as storms develop in the drier air. Some potential for large hail may also exist if storms can persist into greater moisture to the east. ...Wendt/Dean.. 07/21/2025 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .