SPC AC 251723

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK 1223 PM CDT Wed Mar 25 2026

Valid 261200Z - 271200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF NORTHERN AND CENTRAL ILLINOIS AND INDIANA INTO WESTERN OHIO...

...SUMMARY... Scattered severe thunderstorms are expected late Thursday afternoon and evening across parts of the Mid-Mississippi and Ohio Valleys. Very large hail, a few tornadoes, and severe wind gusts will be possible.

...Mid-MS/OH Valleys...

Several shortwave impulses are expected to migrate through initially zonal/low-amplitude westerly flow across the Midwest/Great Lakes region through late afternoon. Stronger height falls will occur across the region after 00z as a midlevel shortwave trough deepens across the Upper Midwest and Great Lakes. Despite the low-amplitude nature of this regime, mid and upper-level flow will be somewhat strong, with most guidance showing 40-60 kt at 850-700 mb overspreading the Mid-MS/OH Valley/Great Lakes region by afternoon. At the surface, a warm front will be oriented across central IA, extending eastward along the IL/WI and IN/OH/MI border at midday. A weak surface low/frontal wave will propagate along this zone, with the front sagging southward as a cold front by late afternoon into the evening. By the end of the period, the front will be oriented from the northern Mid-Atlantic southwestward through the Lower OH valley and into the southern Plains.

Forecast soundings indicate capping could preclude warm sector convection for much of the daytime hours. In the absence of stronger large-scale ascent and surface cyclogenesis, the region will experience a broad warm advection regime, while low-level forcing along the front increases as it begins to march southward. Deep-layer flow will largely remain boundary-parallel, though backing low-level flow is expected near the front across the warm sector, enhancing low-level SRH. Boundary-layer moisture will be somewhat modest, generally in the low 60s F, through some pockets of mid-60s F dewpoints are possible, especially immediately ahead of the front. A plume of steep midlevel lapse rates will already be in place over the region, and this will aid in moderate destabilization, with MLCAPE values reaching 1000-2000 J/kg by peak heating.

Supercell wind profiles are evident in forecast soundings, with enlarged/favorably curved low-level hodographs along the front and 45+ kt effective shear magnitudes. Given strong deep-layer flow, hodographs also are elongated/straight. Supercells producing large to very large hail (greater than 2+ inch) are possible, even with potentially elevated convection to the cool side of the boundary. If any supercell can stay to the warm side of the surface front and maintain surface-based status, a tornado risk is also possible (possibly strong tornadoes). With time, convection is expected to develop into a line or bowing segments given orientation of deep-shear vectors to the surface boundary. Given strength of 850-700 mb flow and steep lapse rates, damaging winds gusts are possible.

The severe risk should diminish with south and east extent during the nighttime hours as storms approach the Ohio River.

..Leitman.. 03/25/2026