I used the observations at Hill City, Russell and Concordia just prior to frontal
passage. I leaned toward Concordia since this location was in the inflow, 40 miles
east-southeast of the tornado at Kensington. At 16 UTC the T/TD were 55F/50F at
910 mb at Hill City and 58F/50F at 924 mb at Russell. At Concordia, dewpoints were
in the mid 50s for 12 hours prior to the tornado that would occur 40 miles to the
west northwest. At 17 UTC the T/TD were 63F/55F at 938mb. With such a progressive
system, it's difficult to determine 700mb/500mb temperatures in the tornado affected
Kensington area at 16 UTC. I am approximating -3C/-21C and using the above surface
parameters, the 700/500mb lifted indices would be -4.5/-6.