Extreme heat, lightning, dust storms (“Haboob’s”), thunderstorms, wildfires, downburst winds and flash floods are a recipe for danger. Combine these seven weather events and you have the making of Monsoon thunderstorms in Arizona.
Starting on June 15th and lasting through September 30th “The Monsoon Season” is a period of extreme heat in the beginning followed by an inundation of moisture that leads into thunderstorms. Arizona gets a third of our annual rainfall during Monsoon season.
A monsoon is caused by warm air creating surface low pressure zones that in turn draw moist air from the oceans. Arizona winds usually come from the west, but shift to a southeasterly wind in the summer, bringing moisture, most often from the Gulfs of Mexico and California. 
As if the heat weren’t dangerous enough here in Arizona, thunderstorms, on top of that, can be deadly. Since 1995, multiple deaths, over 100 injuries and millions of dollars worth of property damage have been attributed to all of the above.
During the monsoon season, ominous thunder clouds are fueled by daytime heating and build up during the late afternoon-early evening. Typically, these storms dissipate by late night, and the next day starts out fair, with the cycle repeating daily.
Rainfall during the monsoon is not continuous. It varies considerably, depending on a variety of factors. There are usually distinct “burst” periods of heavy rain during the monsoon, and “break” periods with little or no rain.
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Flash floods are dangerous to drivers, hikers, and people near washes. Winds almost always exceed 40 mph and can create dust storms. Hail usually occurs in the mountains but the Valley has seen it’s share over the years too (see video below). Excessive heat is dangerous during the monsoon season, as it is all summer. High temperatures can be more dangerous when combined with the high humidity.
Be safe during the monsoon season! Homeowners who live in flood areas should take necessary precautions to protect themselves and their homes, and drivers should never enter flooded areas. Hikers and campers should avoid canyons with steep sides. If thunder is audible, lightning is close and it is advised to go indoors and remain there until 30 minutes after the last lightning sighting. Be sure to avoid downed power lines. Dust storms are often an underrated danger. Dust storms are especially dangerous to drivers. If caught in a dust storm, immediately pull off the road, turn your car off, and take your foot off the brake pedal. 
To be prepared for the Monsoon season read the safety tips here.
For more and up-to-the-minute info on monsoon season in Arizona, visit these links.