Severe thunderstorms are expected on Tuesday from the Mid/Upper Mississippi Valley into the Central/Southern Plains. The highest risk is forecasted for eastern Nebraska, western Iowa, and southwest Minnesota, where there could be very large hail, severe wind gusts, and a few tornadoes. Further south in from Kansas to Texas, a few storms will likely form posing the same threats but in a more isolated manner.

Locations:

  • Primary Risk Areas: Eastern Nebraska, western Iowa, northwest Missouri, eastern Kansas, southeast South Dakota, and southwest Minnesota.
  • Secondary Risk Area: Western Oklahoma into Northwest Texas.

Threats:

  • Very Large Hail: Potential for hail greater than 2 inches in diameter.
  • Severe Wind Gusts: Gusts potentially in excess of 75 mph.
  • Tornadoes: A few tornadoes possible, particularly with stronger supercells in the primary risk area. The tornado risk in the secondary risk area is non-zero but very low.

Timing:

  • Peak Activity: Tuesday afternoon and evening.

Discussion:

Weather Patterns: A significant mid/upper-level shortwave trough will progress eastward from the Northern Rockies into the Northern Plains on Tuesday, with a strong jet streak enhancing the dynamics over the Central Plains.

Atmospheric Dynamics:

  • Moisture and Instability: Modest low-level moisture will move northward from the Southern to Central Plains and Upper Mississippi Valley. Dewpoints ranging from the 50s to near 60°F could extend as far north as eastern Nebraska and western Iowa by Tuesday afternoon. This moisture, under steep midlevel lapse rates, will support diurnal destabilization, with peak MLCAPE values from around 500 J/kg in southern Minnesota to over 1500 J/kg in the Central/Southern Plains.
  • Storm Development: Expected storm initiation along a cold front by mid-afternoon across northeast Nebraska into southeast South Dakota, with later development possible further south into southeast Nebraska and northeast Kansas as strong ascent interacts with the region.
  • Severe Potential: Supercells could quickly form due to favorable deep-layer shear, though evolution toward a linear or cluster mode is possible as storms move eastward. Large hail greater than 2 inches in diameter and severe wind gusts over 75 mph are possible, especially if storms undergo notable upscale growth. The tornado risk, while present, will depend heavily on the quality of low-level moisture, which is currently uncertain.
  • Practical Tips:
    • Target Area: Focus on the initiation zones along the cold front where diurnal heating maximizes instability before storm onset.
    • Safety and Preparedness: Maintain a safe distance and have exit strategies planned. Monitor updates on storm development and potential mode shifts from supercells to linear structures, which can alter the nature of the threats.

Technical Discussion

In the primary risk area across Iowa/Minnesota/Nebraska, a couple of supercells will emerge with large hail, damaging winds, and a tornado threat in the late afternoon. In Kansas, a storm or two will also take shape, with favorable ingredients for a supercell or two.
The secondary target will also see storms, but their nature is a bit uncertain today. If a supercell can form here, it will pose the threat of very large hail and damaging winds, along with an evening tornado threat. This is the type of day that can yield a tornado or two around the sunset hours as a supercell ramps up its low-level mesocyclone with the increasing LLJ.