Okay, I've seen this too much now. I don't want to sound like a total @$$, but I wish people would stop calling every single storm they chase a supercell. I don't know for sure about the South Dakota ones, but I know the SE NE storm was not a supercell. It was pretty much a pulse severe ordinary cell. Perhaps it showed weak rotation briefly, but that storm did not fit the Doswell definition of a supercell. A supercell is a storm with a deep, persistent, rotating updraft, and the rotation has to be significant. Most individual thunderstorms rotate to some extent, but supercells have a mesocyclone, which I know the SE NE storm never had.
EDIT: After appearing too sound hasty, I decided to take a much more detailed look at the storms. I pulled up some archived Level II data and found that the SE NE storm showed weak rotation at one isolated elevation scan on two consecutive scans. The storms up in SD did rotate a little more, but still the rotation was marginal at best. I had to look long and hard to find one scan with a max shear of about 45 knots for one scan and only at one elevation scan. There was some correlated rotation, but it only lasted about 3 scans. One storm west of Sioux Falls (much later) actually showed about 55 kts of shear and rotated at about 4 consecutive elevation angles. It was buried in a line, though, and the rotation was somewhat small in size and somewhat transient, so I'm thinking it may have been more of a mesovortex than an embedded supercell.
EDIT: After appearing too sound hasty, I decided to take a much more detailed look at the storms. I pulled up some archived Level II data and found that the SE NE storm showed weak rotation at one isolated elevation scan on two consecutive scans. The storms up in SD did rotate a little more, but still the rotation was marginal at best. I had to look long and hard to find one scan with a max shear of about 45 knots for one scan and only at one elevation scan. There was some correlated rotation, but it only lasted about 3 scans. One storm west of Sioux Falls (much later) actually showed about 55 kts of shear and rotated at about 4 consecutive elevation angles. It was buried in a line, though, and the rotation was somewhat small in size and somewhat transient, so I'm thinking it may have been more of a mesovortex than an embedded supercell.
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