There is lots of great riding in the Southwest, but if you go too early in the year, you can still hit snow in the Rockies or even the north rim of the Grand Canyon - but the desert will be pleasant. If you go later, then you'll have temps above 100 degrees in the desert areas, but the higher elevations will be real nice. Go even later and it will be hot and humid and you will hit thunderstorms in the afternoon in the higher elevations.

 

What months are you talking about for each scenario? If you don't mind.