Monsoons are primarily manufactured over northern Mexico from moist pacific air mixing with hot and dry Sonoran air*. The moist/dry air is converted almost instantaneously to clouds, which follow the onshore path and dump the precipitation over Arizona and sometimes Utah. If any of it gets past Phoenix it can make its way all the way to Kanab. BOOM! Lots of thunder and lightening and lots of rain. And I really mean RAIN! It can dump one inch of rain here in 30 minuets or less.

* Occasionally a Gulf of Mexico Hurricane can send summer moisture into the Four Corners area and they too will be called monsoons. However the best way to differentiate between a Sonoran monsoon and a Gulf rain is to note the path on satellite photos. Additionally Gulf storms come ashore as already moisture laden clouds while Sonoran monsoons are created over the Mexican desert from, what can be, cloudless skies.