Severe thunderstorms are fairly common during the monsoon in Arizona.
Weather Patterns Associated with Severe Thunderstorms. The streamlines depicted below are for the mid-levels or about 20,000 feet above sea level. A broad high is positioned across the southern half of the United States with easterly flow located over portions of Texas, New Mexico, Arizona and northwest Mexico. Easterly flow in Mexico means lots of thunderstorms in the mountain foothills. The Type II pattern is associsted with a high amplitude ridge over the western United States.