June 17th had a short wave trough moving across the northern high plains. Decent moisture and instability was in place to fuel significant storms. However a capping inversion kept storms from forming until late in the day. A storm complex moved out of Montana into eastern Wyoming, and it was this complex that developed significant rotation as a storm in front of the line became absorbed into it and caused it to rotate rapidly. A tornado warning was issued for the western Black Hills as the storm approached Beaulah and into the Spearfish area. The structure as dusk was quite nice and the lightning was amazing! One of the best lightning displays all season so far!