The average date of the last frost in Fargo-Moorhead over the past three decades is May 8.
This date is a few days earlier than it was a few decades ago. One subtle advantage of the warmer climate is that our average growing season is a few days longer than it used to be.
However, the average of anything is nothing other than the mean, the middle and the center. Average last frost is in no way supposed to signal anything about when the last frost is "supposed" to happen. Some years, there is no frost at all in May, and the final frost happens in April.
Last summer, there were patches of light frost the morning of June 26, although it only reached 40 degrees in Fargo-Moorhead. The latest officially recorded freezing temperature in Fargo is June 20, 1969.