July 24, 2002 - Southeast South Dakota

  
Chase Account by: Jonathan Garner
 
Brian Thalken, Jim Kaiser and I made it up to Sioux Falls, SD by 2:30 pm today, and then made our way west toward Mitchell, SD. At around 3, we drove 10 miles south to investigate several large cells developing along the SD/NE border. We decided not to pursue these and instead decided to target another cell northwest of our location (a few of the cells south of us went on to become fairly impressive supercells later in the evening in Nebraska). By 5:45pm we were closing in on the cell which was located in Jerauld County, SD (northwest of Mitchell). A large mid-level inflow shelf was present streaming into the updraft, with a large, white, expansive anvil towering above the updraft. We were still at least 20 miles from the base of the storm, but we could see the rain free base, which was beginning to widen and showing hints of developing a wall cloud. So we decided to move in closer so we could be in position for any tornadic activity. As we were driving toward the base, we learned of a tornado warning being issued for this storm, which seemed to be warranted given the mid-level rotation which we were observing.

By ~6:30-6:45pm, we reached the base (we were now ~5 miles from the storm), just in time to watch the wall cloud really get its act together. A long inflow tail rapidly developed and was rotating cyclonically around the low-level mesocyclone...this was incredible to watch. The updraft was also extremely photogenic, and was taking on a classic horse-shoe shape, with a laminar appearance at the base curving back toward the southwest. During the next 15 minutes the wall cloud continued to develop, and rotation was really tightening up. We were hoping to see an RFD make an appearance, which would have been a sure sign of imminent tornadogenesis. Unfortuanetely, just when a tornado appeared to be a sure thing, the storm couldn't maintain its forward flank outflow anymore, and a cool gust front rapidly surged south...oh well. Regardless of the fact that a tornado wasn't produced, this chase was still an outstanding experience. The structure this supercell displayed was awe inspiring...definitely one of my top chases.