High Plains Drifter

I’m sitting along hwy 37 between Parkston and Tripp, SD (south of
Mitchell), where there is a very moist southeast wind temperature
around 90 and a dewpoint around 73 to 75 degrees with surface-based
cape exceeding 5,000 J/kg. Extreme instability right now, and I am
monitoring some surface based cumulus growth to my west and southwest,
with an initial small storm trying to develop just south of Lake
Andes. This may be the start of the show. Tornadic supercell is
likely in this environment early this evening across far southeast
South Dakota, perhaps near Sioux Falls.