This area of hot temperatures corresponds well to the HRRR temperature statistics I computed on the Open Science Grid. Below is a HRRR zero-hour forecast valid 1800 UTC on May 30, 2018. The black contour is the 500 hPa geopotential height and the red shading shows how many degrees the HRRR forecast was greater than the 95th percentile temperature for the previous 3 years.
