June 20, 2021

June 20 looked like a pattern recognition type chase, a classic “don’t get suckered into Iowa” type of day. I expected a morning MCS to move through the warm sector and suppress the northern progression of the warm front, but for the warm sector to recover and the warm front to be the main play later in the day. I had seen this same event unfold a dozen times before.

Brindley and I met up in the afternoon and planned on a northeastern Illinois target along I-80 from Ottawa to Kankakee. Cloud cover was hampering the area, while Iowa looked like it was destabilizing. This is how it always plays out though just before you get baited west. We held our ground. The warm sector did not recover, however. A narrow tongue of instability along the I-57 corridor was all that remained going into the early evening and then even this was snuffed out by gust fronts and junk convection. We pushed into Indiana trying to make any kind of play on a storm, but it was too late and we wound up intercepting nothing. The Iowa target produced and the daytime Illinois target was shutdown. We called it and split for home.

Overnight, a damaging EF3 tornado tracked through Woodridge, just a few miles from my childhood home, and where my dad was a police sergeant. There was some debate among meteorologists about what kind of tornado it was with some claiming it to be a QLCS or mesovortex type tornado, and I agreed after a quick look at the radar. Jon Davies suggested it was supercellular with an embedded supercell and mesocyclone evident on radar. A closer look at the velocity data did show an occluded mesocyclone and large supercell in the mix. However, it appeared that the circulation that went on to produce the Woodridge tornado was actually located on the apex of the RFD gust front and gust front intersection from the training cells ahead of the supercell (white circle below black circle). The supercell’s mesocyclone (black circle) looked like it was occluded behind the main gust front to the north of where the tornado formed. There were several other circulations that formed on gust front intersections (white circles) and some of these also went on to produce tornadoes including one near Romeoville. This would indeed make it more of a QLCS type tornado rather than one associated directly with a long lived supercell mesocyclone.