June 11, 2008 Ashton, IA Supercell

This was the make-or-break day for the short private tour. The tornado potential appeared to be pretty good in northwest Iowa, and in adjacent parts of MN, SD and NE. We departed Winner around 9 a.m. and had lunch in Sioux Falls. From there we drifted south and east into extreme northwest Iowa. By around 3 p.m. storm towers erupted along the SD/IA border, just to our west. We were in great position near Sheldon. All we had to do was choose the right storm…the problem was that there seemed to be dozens to choose from! Well, not that many, but the storms were rather bunched up from Sioux Falls down to Omaha. We picked the easiest one, just west of Sheldon. As we observed its approach towards Sheldon, another cell down the line to our south maybe 30 miles looked better and became tornado warned. I decided to quickly dart east and south, but minutes after this decision was made, a tornado warning was issued for the Sheldon storm! It had not looked that great five minutes earlier, but the Doppler radar must be seeing strong rotation. We went back west and then NNE on Route 60 towards Ashton. The cell just a mile or two to our west had a great look at low levels, with an obvious RFD cut and rotating precip curtains beneath a prominent lowering. We were just south of Ashton, and I had the feeling that the town was in big trouble. The circulation came up to the town and was right on our heels as we continued NNE on 60. The low levels were unable to wrap up tightly, however, and in minutes the cell was an HP blob. The storm may have been briefly and weakly tornadic, but the best we observed was the broadly rotating wall cloud and fast-moving precip curtains around it.

Thereafter we managed to intercept several other tornado-warned cells in northwest Iowa, and even near Worthington in Minnesota, but the storms were messy and rainy. We were a little late for the cell that was tornado-warned near Spencer. Another one came up to Emmetsburg, with briefly interesting structure in low light. And, as we reached Laurens a cell was tornado warned — right at Laurens. There were a few good CGs and little else significant with it. The big event of the day was a few counties farther south, near Blencoe, IA, where four were killed by a tornado that hit a Boy Scout camp.