947 ACUS02 KWNS 271733 SWODY2 SPC AC 271732 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1232 PM CDT Sun Jul 27 2025 Valid 281200Z - 291200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL MONTANA INTO WESTERN WISCONSIN... ...SUMMARY... Severe thunderstorms are possible from the northern Rockies into the Dakotas and Upper Midwest Monday afternoon and evening. Large hail and damaging/severe wind gusts are expected. Isolated intense gusts to 85 mph may occur from eastern South Dakota into southern Minnesota. ...Eastern SD into WI... A favorable pattern for a damaging wind event is evident on Monday from central/eastern SD into southern MN, far northern IA and portions of WI. A 10 percent significant wind area has been delineated and the Slight risk (level 2 of 5) has been expanded eastward. However, some uncertainties remain (related to Day 1/Sunday convective evolution), precluding a categorical increase to Enhanced risk (level 3 of 5) at this time. Enhanced westerly flow is forecast across the northern Plains vicinity as a series of shortwave perturbations float through the top of the upper ridge from the northern Rockies into the Upper Midwest. At 500 mb, 40-60 kt westerly flow will be common. At the surface, a very moist (mid/upper 70s dewpoints) airmass will be in place. A plume of steep midlevel lapse rates are also evident if model forecasts. This combination of a very moist/warm boundary layer beneath steep lapse rates will support a corridor of strong to extreme instability (3000-5000+ J/kg MLCAPE) from eastern SD into southern MN/northern IA and southwest WI. A surface low is forecast over southern SD/northern NE. A cold front will develop south/southeast across the Dakotas and Upper Midwest. A modified outflow boundary from Day 1/Sunday convection also will likely be in place across parts of MN/IA/WI, though where this boundary will be is uncertain at this time. The surface low will be a focus for initial robust thunderstorm development in SD during the afternoon. With time, upscale growth is likely to occur as a modest low-level jet develops during the evening. Convection will likely develop east/southeast along the instability gradient defined by prior outflow and the southward sagging cold front. Initial thunderstorms could produce large hail and damaging gusts, with a transition toward damaging/severe wind swaths if/when upscale growth occurs. The main uncertainty precluding higher probabilities is related to how Day 1/Sunday convection will impact the boundary layer and where related outflow and airmass recovery will occur. Higher probabilities may be necessary in subsequent outlooks. ...Montana into the western Dakotas... Isolated to scattered thunderstorms are expected to develop within the post-frontal upslope regime where boundary layer moisture in the mid 50s to mid 60s will persist behind the surface boundary. Strong heating and steep midlevel lapse rates will support 1000-3000 J/kg MLCAPE values (from west to east) amid elongated/straight hodographs. Large hail and isolated strong/severe wind gusts will be possible with this activity. ..Leitman.. 07/27/2025 $$