April 19, 2011 IL Storms

Yesterday started out in Geneva, IL; where I and a friend met up with two fellow storm chasers. I had a preliminary idea of where I wanted to head, and we confirmed that as we traveled south towards Springfield, IL. We knew where the track of the Sfc-Low was going to be, and with that track, the best backed surface winds were going to be in that vicinity. That meant we had to hang relatively close to the warm front where this enhanced helicity and shear would be. Right off the bat, we knew moisture was not going to be a concern. Sfc dewpoints ranged from the low 60's to low 70's, with a very impressive pool of 60+ dewpoints at 850mb (~1.5km). We decided on Litchfield, IL for a target area. As we drove just south of Springfield, we finally got south of the Warm Front, and that was where our extensive stratus deck finally ended. Temperatures climbed rapidly within the next 30 miles; going from a mere 61 to a high of 78. We sat at McDonalds in Litchfield watching our setup. Around downtown St. Louis a boundary of some sort had set up (moisture boundary!?), and was evident with radar loops. This was one of our main focuses because of it possibly being the cap breaker. Instead storms started initiating ahead of the cold front, close to a triple point. They were WNW of St. Louis. We watched the scans come in on those cells, and quickly decided to head towards Carrolton, IL across the river from a cell that was going "super" quickly as it headed towards Bowling Green, MO. That cell looked beautiful on radar; but it would not hold.



As that cell hit the Mississippi River bluffs on the IL state line, it fell apart. It went from a supercell to what we described as "blobish". We continued to follow the cell, and experienced two Gustnados, but unfortunately, the cell looked to be gusted out, with a forming shelf cloud.

We quickly traversed back towards Carlinville, and noticed that our original player (convergence along that radar viewable boundary) had initiated a supercell. There were a few wall cloud reports coming off the cell as we headed towards it. As we approached, we saw a visible wall cloud and tightening rotation in the low level mesocyclone. And as we headed east on IL-108, that cell developed a small funnel cloud eventually making a brief touchdown. Within seconds, the RFD ramped up on the south side of the storm, and a very low inflow tail developed on the north side of the mesocyclone south of the FFD. The inflow coming into the cell went from mere 20 knot winds to 60+ knot winds in a matter of no time. We got to the junction of I-55 and IL-108 which provided a perfect vantage point for this storm. SSW of the Pioneer seed plant, the storm started to produce a classic cone shaped funnel cloud, with the start of debris showing near the ground as well.

The funnel cloud finally made full contact with the ground, putting up a rather large debris cloud. We were viewing this tornado from ~ 1-1.5 mile(s), and even at that distance it looked large! It became more defined as it moved ENE across I-55. After about a mile or so east of I-55, it finally lifted a bit as it started progressing into an HP Supercell.







We continued to try to get ahead of this storm, but unfortunately we encountered quite a bit of traffic, which slowed us down greatly. Eventually the cells quickly developed into a rather large derecho, moving at an unbelievable pace. There were still embedded supercells within this system, but most of them were dealing with heavy rain wrapped precipitation, thus making it far more dangerous to chase. We eventually took shelter in Greenville, IL off of I-70, and after the line passed, we headed back home.

Here's the Double Derecho!