Why no tornados in west usa?

Conditions are not right for tornado formation west of the Rocky Mountains. In order to get tornadoes, you need warm, moist air coming in at lower levels of the atmosphere, warm dry air in the mid-altitudes, and higher up, cold dry air. Also, you need wind shear, or change in wind speed and direction as you go up into the atmosphere. The conditions are much better for tornado formation in the Great Plain States because they have the warm, moist air from the Gulf of Mexico, the warm, dry air from mainland Mexico, and the cold, dry air from the Rockies.