Several strong wedge tornadoes occurred yesterday in IL and IN. What went right with yesterday's tornado outbreak? To me, the biggest synoptic driver was the nature of the elevated mixed layer of air, or EML. Models yesterday morning (HRRR, RRFS, NAM) progged this layer of air to be cold and moist throughout peak heating later in the day. This would lead to a large layer of poor lapse rates between 850mb and 650mb and feature a "warm nose". A warm nose like this with high deep-layer moisture content is a hallmark for struggling updrafts and destructive mergers in a sloppy storm mode- in my opinion, the biggest failmode for yesterday. While forecasting, I noticed that a much more stout and classic EML was modeled to be present by mid-afternoon back into Missouri and points south and west. However, guidance did not indicate this would fully and cleanly advect into the favored area for lift and shear (and thus storms). However, observations told a different story. The 1pm Lincoln, IL sounding showed this warm nose profile with weak low level lapse rates and a moist mid-level profile (ignore upper levels- anvil debris from prior storms). However, by 4pm, another Lincoln, IL sounding suddenly showed a loaded gun, a stout capping inversion and somewhat decent EML atop with drier air aloft than modeled. This prevented the warm sector from producing messy meager updrafts along the strong confluence boundaries present and instead fostered more explosive updrafts once weak storm-modified environments broke through this capping inversion (and as the main trough forcing increased later in the day along with diurnal heating). So in essence, the nature of the EML being a true capping inversion rather than a warm nose cleaned up the warm sector substantially from a messy mode to a more semi-discrete to discrete dominant mode, seen pretty clearly in the HRRR to MRMS comparison. One other driver to point out was the *benefit* of the midday line of storms being stronger/further south than anticipated. This placed a stronger boundary further south, which was still allowed to modify under the June afternoon recovery. While perhaps some better dynamics and shear was present further north into Iowa and Wisconsin, that capping inversion had no chance of advecting that far north, so it was guaranteed to be a messy mode with competing updrafts. Instead, stronger mesoscale dynamics induced by the outflow left behind by the midday round and reduced vertical mixing from the midday round allowed hodographs to retain stronger low level curvature and shear, and consequentially sweep higher SRH. This was exacerbated so much that winds were actually backed out of the east at the surface in reality when the stronger mixing that was modeled veered hodographs out of the SW, substantially increasing low level directional shear too. With these changes in mind, the mesoscale came together with interactions between just the right amount of surface confluence well out ahead of the cold front balanced with the capping inversion and the effect and motion of the remnant outflow boundary set by the midday round of storms on 0-1km SRH and stretching potential. And born from this were multiple (likely) significant tornadoes. Definitely verified the SPC forecast, albeit a bit SE of initial expectations. (see replies for additional graphics)

This allowed those Peoria cells to take root in an unstable yet clean environment way far ahead of the cold front.