Brief Outlook:
Severe thunderstorms are expected across parts of the Upper Midwest and Mississippi Valley, particularly in Iowa, Illinois, Indiana, and Kentucky, from the afternoon into the evening. The main risk with these storms will be damaging winds, large hail, and isolated tornadoes, with a concentration of damaging winds.
Region Impacted: Upper Midwest and Mississippi Valley
States and Cities Impacted: Iowa (Des Moines, Cedar Rapids), Illinois (Chicago, Springfield), Indiana (Indianapolis, Evansville), Kentucky (Louisville, Lexington).
Upper-Level Dynamics:
A broad upper trough with embedded shortwaves will influence the Upper Midwest and Mississippi Valley. Enhanced westerly flow, resulting from this system, will interact with the existing upper ridge, creating strong vertical wind shear, with values around 35-45 knots in the 0-6 km layer. This will support organized storm structures capable of producing severe weather.
Surface Conditions:
At the surface, instability values are expected to reach 3000 J/kg (locally higher), particularly across Iowa and Illinois. Dewpoints in the low 70s will contribute to significant instability. Effective shear will support supercell development, and steep mid-level lapse rates will promote strong updrafts. Initial storm modes are expected to be discrete, with a potential transition to clusters or lines, eventually an MCS expected to form with wind gusts sometimes reaching over 75mph. These storms will be capable of producing large hail and damaging winds. Isolated tornadoes are also possible, especially in regions with enhanced low-level shear is present across portions of northern IA.
Timing:
Thunderstorms are expected to initiate by late afternoon in Iowa becoming severe very quickly, moving into Illinois, Indiana, and by the late evening. These storms will continue to move southeastward throughout the overnight as an MCS with multiple clusters. Peak activity will likely occur from late afternoon through the late evening in multiple rounds, with the most severe storms expected during this period.
Future Radar Scenario:
Main Impact: damaging winds, large hail, isolated tornadoes and lightning.
Stay tuned for more updates.
Sina⚡⚡
Managing Partner and Lead Forecaster of NWF Innovations & NWF Networks