Severe thunderstorms, including several tornadoes, are expected this afternoon to early evening, primarily across Iowa and adjacent parts of southeastern Minnesota, Wisconsin, Illinois, and Missouri. Further south, more severe storms will be possible with hail, damaging winds, and a tornado or two. 

Locations:

  • Primary Risk Area: Much of Iowa and nearby parts of southeastern Minnesota, Wisconsin, Illinois, and Missouri.
  • Secondary Risk Area: SW Missouri, Eastern Oklahoma, Central Texas

Threats:

  • Tornadoes: Several tornadoes, some strong (EF2+ damage potential), are possible, especially in the primary risk area.
  • Large to Very Large Hail: Likely with initial supercells.
  • Severe Wind Gusts: Potential for destructive wind swaths of 80-100 mph, with localized extreme gusts exceeding 100 mph.

Timing:

  • Storm Initiation: Midday to early afternoon in the northern target. Late afternoon and early evening in the southern target.
  • Peak Intensity: Afternoon to early evening.

Meteorological Discussion:

500wh.conus 8.A large trough is moving over the middle of the country today, which will be the spark for storm formation throughout the middle of the country into the Midwest.

Synoptic Setup:

  • A slow-moving cyclone will meander over southern Saskatchewan, while a separate closed low digs southeastward from northern British Columbia to Washington.
  • A mean trough will extend from the northern Rockies across southern California and offshore northern Baja.
  • A shortwave trough over the High Plains will pivot northeastward to southern Minnesota, central Iowa, and northwestern Missouri by 00Z, reaching western and northern parts of the Upper Great Lakes by 12Z tomorrow.

Sfctd_b imp.conus 7.A large surface low over the midwest will help back winds and push a cold front south. 

Surface Analysis:

  • At 11Z, lows were near SUX and CNK, along a cold front arching to southwestern Kansas and the Raton Mesa.
  • These lows will consolidate into a coherent cyclone center and move to southern Minnesota by 00Z, with the cold front extending to southeastern Iowa, central Missouri, and central Oklahoma.
  • A dryline from west-central Kansas will shift eastward over southern/central Oklahoma and northwest/west-central Texas.

Storm Development Regions:

  • An ongoing band of thunderstorms will sweep across Iowa this morning, with severe gusts, large hail, and a few tornadoes possible.
  • The main event will occur midday through the evening, with scattered to numerous thunderstorms, including multiple fast-moving supercells, forming over eastern Nebraska and moving into Iowa and northern/central Missouri.

Storms will line out from Wisconsin to Oklahoma. More isolated storms will be eastern OK into Texas.

Storm Modes and Evolution:

  • Supercells capable of producing very large hail, tornadoes, and severe downbursts are expected.
  • Several rounds of convection may cross the region, transitioning to clusters and linear bowing segments with potential for intense rear-inflow jet development.
  • The low-level jet will strengthen during the evening, supporting a large MCS with embedded bowing structures.
  • The primary severe threat will be over Iowa, with potential spreading into southern Minnesota, western/northern Illinois, and Wisconsin.

Key Factors:

  • Large-Scale Ascent and Low-Level Lift: Both will increase across the outlook area throughout the afternoon and evening.
  • Boundary Layer Destabilization: Supported by surface heating and warm advection, with MLCAPE values of 2000-3000 J/kg expected over much of Iowa.
  • Hodographs: Large hodographs with effective SRH exceeding 300 J/kg near and north of the remnant outflow boundary, supporting tornadic supercells.
  • Capping Influence: A capping inversion will limit convection initially to the south, but strong heating and frontal/dryline lift will weaken MLCINH by mid/late afternoon.