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Monsoon Season in Arizona

Arizona is well known for having over 300 sunny days per year, but in summertime, the clouds build and the desert drinks in as much precipitation as possible during the monsoon season. Get to know the magic and the hazards that this time of year can bring.

When is Monsoon Season?

Before diving in, get a lay of the land when it comes to Arizona’s monsoon season. What does “monsoon” even mean, and when does Arizona’s rainy season start? 

From a climate and meteorology perspective, the monsoon season begins June 15 and continues through September 30 each year. Longtime residents of Arizona who know that storms may not begin until closer to July may find this start date rather odd. It helps to understand that June 15 is not a date of prediction for precipitation, but rather a historically observed average date of the beginning of a shift in prevailing winds from a dry westerly flow to a moist southerly flow.

During this time, upper atmospheric pressure builds, and with the influx of moisture that the wind shifts bring, these conditions promote thunderstorm activity, mainly over the mountainous regions where air is forced to rise.

If the wind shift usually starts in mid-June, when does the monsoon rain actually arrive in Arizona? July and August are usually Arizona’s two hottest months, and also the timeframe in which our state typically sees more than half its precipitation that we receive each year. However, not every year has an active monsoon season, and low desert dwellers are anxious for a good rainstorm. Stay informed on monsoon outlooks and become better acquainted with monsoon terminology and available data at the Arizona State Climate Office, which offers monthly weather webinars.

Beauty and Benefits of Monsoon Storms

When the rain does come during Arizona’s scorching summer months, locals rejoice! The fragrant scent of creosote bathes the desert, and windows fly open to listen to the uncommon sound of raindrops falling and thunder rolling. Apart from providing sweet relief to Arizonans longing for rain, the ecological benefits of the monsoon are numerous. The precipitation replenishes groundwater, brings relief from extreme heat, supports wildlife with life-sustaining water, and pushes desert plants into bloom. 

But the monsoon season isn’t all bliss. Storms bring hazards to people and the landscape, of which residents and visitors alike should be aware.

Monsoon Safety Tips for Arizona's Outdoors

As beautiful as Arizona's monsoon thunderstorms are, they are also powerful and unpredictable. Adverse conditions can include dust storms, lightning that can spark wildfires, and flash floods with heavy debris flow. Read on to learn how to stay safe in the hazardous conditions that monsoon storms can create, because in monsoon weather, safety’s clever!

During Arizona’s summer monsoon thunderstorms, flash floods develop quickly and bring danger from rapidly flowing water and debris that can carry away people, vehicles, roads, and even structures. Our state’s arid climate receives a scant amount of rainfall annually and is currently in a decades-long drought. Because of these factors, the soil cannot absorb the copious amount of precipitation that can fall in a short amount of time during a monsoon storm. 

Natural areas and parks can encompass creeks, washes, and fire-scarred terrain, such as Catalina State Park, through which the Canada del Oro and Sutherland washes flow and which contains areas of the fire-scarred Catalina Mountain foothills from the Bighorn Fire of 2020. These areas are especially susceptible to flash flooding. Slot canyons are another area to be extremely cautious about recreating in during the summer months. A storm even miles away can channel high and extremely fast-moving waters through canyons.

Campers and hikers should take extra care when selecting locations to recreate. Avoid low-lying areas, washes, or flood-prone zones. Never attempt to cross a flooded trail or roadway. Turn around, don’t drown! Fast-moving water is extremely dangerous—just six inches can knock an adult off their feet, and just 12 inches can carry away a vehicle.

Arizona commonly ranks in the top half of states with lightning casualties, according to the National Weather Service. The greatest frequency of annual strikes occurs in the higher terrain of southeastern Arizona and along the Mogollon Rim and the White Mountains.

Remember, when thunder roars, go indoors! Pausing your outdoor recreation is a small price to pay for staying safe from lightning. If you hear thunder or see lightning, stop your outdoor recreational activity and go indoors or into a vehicle. More than 60% of strikes are attributed to leisure activities, and a third of those are connected to water recreation. Get off the water and avoid open shelters like shade ramadas, fields, beaches, hilltops, and tall objects like trees. If shelter is not available, avoid open areas, stay at least 100 feet away from metal, including your trekking poles, and crouch low to the ground while remaining on your feet. Wait at least 30 minutes after the last thunder before resuming outdoor activities.

Unfortunately, lightning strikes can also ignite wildfires, though human-caused fires still account for 80-90% of wildfires in the state each year. To prevent loss, be firewise and keep the perimeter of your home clear of brush and debris, especially if you live in a Wildland Urban Interface (the zone of transition between unoccupied land and human development).

Dust storms or even haboobs—giant walls of blowing sand and dust—can develop in the early monsoon, especially over agricultural areas. If outside recreating, remain calm as you move away from peaks, cliffs, or areas of high terrain where strong winds can cause you to lose balance. Cover your nose and mouth with a dampened bandana, neck gaiter, or other material to reduce dust inhalation. If driving, pull aside, stay alive. While riding a designated trail in an off-highway vehicle, bring your vehicle to a stop, taking care not to park over dry grass or brush, which can ignite if in contact with a hot vehicle engine. See additional safety precautions to take while driving on roadways in a dust storm from the Arizona Department of Transportation.

Rising temperatures in the summer are the catalyst for the low-pressure system that results in the wind shift and associated monsoon. Parts of Arizona are some of the hottest places on the planet from May to September. Until the rain comes and lowers the extreme temperatures, it is critical to protect yourself from heat-related illness. Hydrate, limit strenuous activity, avoid being outside during the hottest part of the day (10 a.m. to 5 p.m.), wear sun protection, never leave pets or children inside a parked vehicle, check on your neighbors, and be familiar with available heat resources, like statewide cooling centers. Find more information about your health when it comes to the heat from the Arizona Department of Health Services.

Stay in the Know

Appreciate the beauty of the monsoon season in Arizona, but be proactive about checking the weather and making smart recreation decisions. Reevaluate your plans if you see storm clouds building, even in the distance, and evacuate an area under threat before conditions become dire. Become familiar with the available resources below so you can learn of timely alerts and warnings. 

If you want to support weather monitoring efforts to help keep your community safe, consider volunteering as a precipitation data gatherer for CoCoRAHS or as an NWS SKYWARN storm spotter. 

Monsoon Resources

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