According to Arizona folklore, the monsoon season will start about a week after the cicadas begin to sing at night. In point of fact, the start of monsoon season in the Desert Southwest is denoted by a shift in the winds and usually begins in mid-June to late-July, depending on which part of the Southwest you are in.

Monsoon is traditionally defined as a seasonal reversing of the prevailing winds, accompanied by seasonal changes in precipitation. The Southwest is famous for its monsoon storms, haboobs (dust storms) and tremendous flash flooding. The prevailing west or northwest winds of winter change in late June or early July and begin to flow from the south or southeast, bringing moisture up from the Gulf of Mexico or Gulf of California.

One other elements is needed to cause these explosive and dynamic storms. Daytime HEATING! Monsoon thunderstorms are convective in nature, which means the storms are powered by intense surface heating. With daytime temperatures rising into triple digits on a regular basis, Arizona, New Mexico, parts of Colorado and Utah, these four states are prime targets for huge thunderstorms that can drop as much as 6-8 inches of rain in just an hour or two causing gigantic flash floods in otherwise dry washes, gulches, valleys and arroyos.

And then there are the haboobs — eerie walls of dust that stretch from horizon to horizon, which advance as ominously as an enemy army. Spawned by parent thunderstorms, outflow winds kick up huge walls of sand and dust from the desert floor, particularly in Arizona and New Mexico. These lens-shaped dust walls have an average maximum wind velocity of over 30 mph and dust may raise to heights exceeding 3,000 feet.

In point of fact, Arizona and New Mexico receive up to half of their annual precipitation during the monsoon season, while seasonal daily thunderstorms in Colorado and Utah bring much needed moisture to the mountains. In the Southwest, lightning has ignited more than 2,300 fires annually between 2001 and 2008, burning on average approximately 277,000 acres per year. Those figures, however, represent a mere fraction of the number of lightning strikes these states get each year. For example, between 1996 and 2005, an average of 673,320 lightning bolts touched down in Arizona each year.

Throughout the history of the Southwest, there are literally thousands of stories of devastation caused by this seasonal shift in the weather. However, it is hard to isolate truly tremendous or legendary monsoon events, because it seems each year, somewhere in the four states, a devastating storm hits. In 2010, record amounts of hail (6 – 12 inches) fell in the small town of Commerce, Colorado, forcing residents to tackle the resulting heaps with snow shovels. Near Flagstaff, dozens of homes were affected by huge mudslides caused by a large thunderstorm dumping rain over a burn area. In 2006, Sabino Canyon in Arizona, received over 6 inches of rain in just a few hours. The resulting flash flood was a massive wall of water, mud, huge boulders, fallen trees and giant saguaro cactus that came crashing down the canyon at 17,000 cubic feet per second. In 1997, a thunderstorm developed over LeChee Rock, about 15 miles away from Antelope Canyon on the Arizona/Utah border. Eleven hikers were touring this popular destination when a wall of water struck. One man survived the flood, while 10 others lost their lives. Eight of the bodies were recovered in Lake Powell shortly after the flood, while two bodies remain lost in a wilderness of slot canyons.

Unfortunately, although meteorology is getting better, monsoon storms are very unpredictable. It’s always a good idea to check the weather forecast before you go hiking, and to avoid narrow canyons, washes or arroyos if a storm is threatening. Of course, lightning is another hazard and can strike without warning as far as 20 miles away from the parent storm. So your best bet is to get your hiking done in the morning, before daytime heating causes the huge thunderstorms to bloom in the sky.

And for a final warning note: Arizona has instituted a Stupid Motorist Law. If you drive into flood waters and have to be rescued, it is a good bet the Arizona will make you pay the cost of any emergency services. In short, be smart and be safe when severe weather threatens.