Is early May too early for I 90 across N US?

We were snowed-in in Laramie when a storm closed down I-80 in mid May after our daughter's graduation from UWYO. She said it snowed there every year during finals week.

It didn't ruin our trip, but it slowed us down for a day.

my friend who lives in Rapid City says that they have had snow in every month but one.
bumpy

It should generally be okay, as the others have said. Once past the Rockies the chances of any significant snow are quite close to zero.

I-90, being one of the most important transcontinental transit routes, in general gets cleared of snow as quickly as possible when it comes. If you're willing to be a bit flexible in delaying a leg of the trip, you could go at most any time of the year, even the dead of winter, and usually avoid seeing much in the way of really nasty travel conditions.

There is a chance that next winter will be colder and longer than typical due to the recent volcanic activity. I doubt it will be another 1816 (the year without a summer), thankfully.

The high country may get snow that late but I-90 isn't that high, and usually won't get much snowing May.

We were once the last vehicle allowed across Vail Pass on I-70 in Colorado due to a blizzard... on the 2nd of May. I-90 is north of I-70 last I checked.

Rob

That would be a good time. Would need to keep an eye on weather over the passes in Idaho and Montana.
You cannot trust Mother Nature any time of the year!