Peoria, Ill. (WMBD) — The Storm Prediction Center has once again placed Central Illinois within a day 3 Enhanced Risk (Level 3 Risk level on a scale of 1-5) for severe weather. Like Friday, all severe hazards will be possible, some potentially significant including strong tornadoes.

Key takeaways

  • A very volatile environment will be in place
  • Severe weather is possible from mid afternoon through late Tuesday night
  • Strong tornadoes, very large hail and destructive winds possible
  • Capping inversion could limit afternoon storm potential.

Scattered thunderstorms are expected to develop across Central Illinois on Monday afternoon north of the warm front. Widespread severe weather is not expected with this round, but storms will be capable of producing locally large hail, heavy rain and frequent lightning. Our biggest concern for severe weather comes on Tuesday afternoon and night.

Compared to Friday’s severe weather event, the ingredients for significant severe weather are even better this time around with more moisture, instability and even better directional wind shear. All of these conditions point to an environment that will be conducive for strong, long tracked tornadoes.

This environment can kind of be summed up using the Craven-Widenfeld Aggregate Severe Parameter (CWASP) which shows values over 75 in Central Illinois.

CWASP is a combination of several different weighted parameters and gives us an idea of just how severe and event can be, particularly with tornadoes. When you look back at past tornado events, 75% of EF-2 or stronger tornadoes occurred when CWASP values were over 65. So, IF storms develop, the atmosphere would seem to favor the development of strong tornadoes. Again, IF storms develop…

The set up for Tuesday is very reminiscent of severe weather set ups over the Central Plains where there is a vast warm sector (area between the cold front and the warm front) with a lot of warm, unstable air beneath a layer of warm air aloft, what we call a capping inversion. On these days, the cap prevents storms from developing allowing the warm humid air to become even more unstable. Storms will then explode along the dry line or a cold front, but every once in a while, a few storms break the cap and develop ahead of these boundaries. Should we see this play out in Central Illinois, any storms that break the cap will be capable of producing significant severe weather.

What is a capping inversion?

A capping inversion, what we commonly refer to as a cap, is a layer of warm and dry air aloft. This layer of warm air aloft will act as a lid on the environment preventing air near the surface from rising thus keeping thunderstorms from developing until something (usually a cold front) forces that air to rise through it.

The cold front is not expected to reach Central Illinois until late Tuesday night or even Wednesday morning, so this front will not be responsible for any storms breaking the cap over Central Illinois Tuesday afternoon. Instead, some model guidance suggest that a small impulse ejecting out of Oklahoma Tuesday morning could provide enough lift to break the cap allowing storms to develop Tuesday afternoon. Should storms develop Tuesday afternoon they would be supercells capable of all hazards, including strong tornadoes.

Once any afternoon and evening storms diminish, there will likely be a prolonged break in any storm activity until the cold front arrives late Tuesday night/early Wednesday morning. Storms along this front will likely come in the form of a squall line capable damaging winds and isolated tornadoes.

Higher resolution model guidance is just now coming within range of this event and the details should become more clear over the next few days. Be sure to monitor the forecast closely so you can remain prepared in the event Tuesday turns into another active day of severe weather.