Click here for an animated loop of the radar reflectivity data
Radar images from the Oglala tornado event are below. The first image (below) shows the storms as they appeared at 5:30 PM MDT, close to the time that the first tornadoes were reported in Nebraska. Though the storm was quite distant from the radar at this time, it exhibited may classic features of a severe supercell, including strong rotation, an appendage (possibly a "hook"), and a bounded weak echo region (BWER).
An hour later, at 6:30 PM MDT (below) we received our first confirmation of a tornadoes in South Dakota. At this time, two tornados were reported on the ground west of Pine Ridge. The Doppler velocity image (below right) shows two areas of high gate-to-gate shear, indicating the possible position of these two tornadoes. The northernmost tornado was within the well-formed hook echo west-northwest of Pine Ridge. Note a second supercell to the southwest of the first storm, just entering South Dakota at this time. This second storm also exhibited a hook echo, and eventually produced a tornado about 5 miles north of Pine Ridge.
At 6:40 PM, the tornadic storm moved into the Oglala area. The radar images below show that the extremely strong low-level circulation was just to the south of Oglala at this time. This coincides well with the damage which was observed in the area...with the most severe damage located just to the south and east of the main Oglala intersection.
The two storms which passed through the Oglala area slowly merged into one storm from 7:00 to 7:45 PM. At 7:50 PM, the storm assumed "HP" supercell characteristics, with much precipitation wrapping around the mesocyclone. Several tornadoes were also sighted at this time near the town of Kyle. In summary, you may want to check out this loop of radar images which demonstrates the evolution of the Oglala tornadic supercell.