I am going in April/May next year too
DH was in the USA this year in April/May and he got Snow, tornados, hail (all while riding a motorbike) and then finally some sun the further west he got. I saw your other thread and the weather on the west side will be nicer but not too hot or cold. DH has been in Vegas at different times of the year and has said that April/May was busier then the other half of the year.