Discussion... Observation of 11z HRRR short-range model indicates a strong bowing severe thunderstorm cluster will develop on the eastern fringes of Wyoming and move into South Dakota. Originally in Wyoming, the storms will start out possibly supercellular before congealing into the bowing line. That said, there will be a more elevated threat of tornadoes in NE Wyoming, then a skyrocketing high wind threat into South Dakota.
11z HRRR doesn't indicate any severe weather for Montana, but does introduce moderate showers and thunderstorms in ragged clusters. Unfortunately, 12z RR and 13z RUC are both updating at this time, so we cannot get their inputs.
In summary, South Dakota has a good threat for severe weather for today.