A Slight Risk of severe thunderstorms exists Wednesday afternoon through Wednesday night across the Lower Missouri Valley. The main threats are large to very large hail and a few tornadoes. Down the dryline in Kansas, Oklahoma, and Texas the risk is much more conditional with diffuse convergence and capping making storms very uncertain.

Location

  • Eastern Kansas
  • Southeastern Nebraska
  • Central Missouri

Threats

  • Large to very large hail
  • Isolated tornadoes (especially near the warm front)

Timing

  • Wednesday afternoon into Wednesday night

Discussion

  • Synoptic Setup: A strong upper-level trough moving across the Western U.S. will drive storm development in the Central Plains. Expect a low-pressure system with a trailing dryline and a northward-moving warm front.
  • Storm Initiation: Storms are likely to form near the surface low and warm front in the late afternoon (around 21Z – 00Z) in north-central/northeastern Kansas.
  • Favorable Conditions for Severe Storms
    • Warm, moist air (dewpoints in the mid-50s) and cool temperatures aloft will promote instability.
    • Strong winds at different levels in the atmosphere (wind shear) will support rotating supercell storms.
  • Southern Extent Uncertainty: A chance for isolated severe storms extends into southeastern Kansas, central/eastern Oklahoma, and far northeastern Texas; however, warmer temperatures aloft may limit storm development in these areas.

The overall surface setup is one that has historically been conducive for severe weather, including tornadoes. A surface low will have a warm front extending to its north and east across NE Kansas with a trailing dryline that goes down through Oklahoma and Texas. The dryline is sharper to the north and more diffuse south.

At 7 p.m. tomorrow, most convective-allowing still don’t have robust storms at the sunset hour. But with the increasing low level jet…

Storms fire on most models near and after dark. The overall question I have is are these things north of the warm front tomorrow. The HRRR above is certainly north of the surface warm front, with elevated hailers across SE Nebraska.

The warm frontal zone is characterized by strong effective SRH values (300+) and ample 3CAPE. Both of these would support a conditional risk of tornadoes if storms can get going at or just south of the front and interact with it favorably. That is certainly the question of the day tomorrow. If storms hold off until dark, it is more likely that you don’t get surface-based convection but rather, elevated convection. This would mean hail is the only threat. My initial suspicion is that a rapidly northward-moving warm front is not unlike a rapidly retreating dryline, and it isn’t typical to get robust convective initiation on either type of boundary.

Further south on the diffuse dryline, soundings show a well-mixed boundary layer in the dryline zone with little capping but high-based storm soundings. The well mixed nature of the boundary layer gives me some pause on declaring the dryline will be absolutely storm free, but the blowtorch SW 850mb winds and the need to mix the dryline so much that you end up with massively high LCLs likely means large hail and the primary risk down here if a storm could even get going. The diffuse nature of the boundary owing to the lack of strong convergence would mean you’d likely need some upper-air support that isn’t going to fully be there tomorrow. It’s a nonzero risk, but I’m not that enthusiastic about the dryline tomorrow. The window for storms is narrow, with a 4-5 p.m. start and an 8 p.m. death. But if a robust cell can somehow materialize, a low tornado risk will be present.