SD experienced "heat wave" these few days. The high along the coast was about 80-85 the last couple of days. Then, temeprature along the coastal area in SD is usually about 10-20 (farenheit) degrees lower than areas that are, e.g., 10-20 miles towards the inland.
So, depending on where he is located in SD, a 100 degree temperature is quite likely for these few days.