Monsoon Season in the Southwestern United States

Summer Monsoon in Southwestern United States, Colorado - Alex Pullen Photography (3 of 3)

Summer Monsoons drift over “The Sleeping Ute” near the Colorado/Utah border. Photo by Alex Pullen

If planning to visit or recreate in the Southwestern United States in the summertime, it’s important to be aware of the afternoon thunderstorms typical of “Monsoon Season“.  This time of year should be associated with afternoon rainstorms and lightning, so be prepared and plan accordingly. 

Anvil top Cumulus Cloud building on a September evening - Alex Pullen Photography

“Anvil Top” Cumulus Cloud building on a September Evening – Photo by Alex Pullen

These fairly predictable storms are caused by a shift in wind patterns, which funnels more moisture from the Pacific Ocean and Gulf of California to the Southwest. Monsoon season typically starts in mid July and continues through the end of August but can persist as late as October. Monsoons play a critical role in the desert and mountain environments of the Southwest by providing much needed water and helping decrease the likely hood of forest fires.

As moisture rich air moves across the desert it heats up and rises creating cumulus clouds (or thunderheads) in the afternoons. These multi-story clouds formations then precipitate anything from a light isolated rain, to intense showers, hail and lightning. Depending on where you are these storms can also create 20-30 degree Fahrenheit temperature swings potentially leaving you soaked, shivering and in a life threatening situation.

Until this year, the National Weather Service (NWS) declared that the monsoon season began on the first of three consecutive days when the average dew point temperature was greater than 54 degrees Fahrenheit in Tucson and 55 F degrees in Phoenix. The average monsoon start date in Tucson was July 3, according to statistics compiled by the NWS for 1949 to 2007. The earliest onset occurred in 2000 on June 17. In Phoenix, the average start date was July 7 and the earliest onset similarly occurred on June 17, 2000. Unlike Arizona, New Mexico has not quantitatively defined the onset of the monsoon.

The dew point temperature, however, is just one of several indicators of the monsoon and it is typically the last index to suggest that the monsoon has arrived, said Eric Pytlak, science and operations manager at the NWS in Tucson.

In June, for example, numerous monsoon storms occurred around Tucson while the dew point remained below 54 degrees F. For this reason, and to allow the media to more effectively communicate to the public when the monsoon storms are likely to form, the NWS in Arizona has designated June 15 as the official monsoon start date.


  • Checking the Weather Forecast – While a recommended practice, do note that in the mountainous areas of the southwest the weather is very unpredictable. Your best bet is to be off of the tops of peaks or climbs in the early afternoon (to avoid lightning), and be prepared to get rained on in the afternoons.
  • Remember “it’s easier to stay dry than get dry” – Monsoonal rains usually don’t last long. If you are in the back country, seek a sheltered place not prone to lightning strike and wait out the brunt of the storm before setting up camp or moving onward.
  • Rain Gear – My father always used to say, “the dumbest man in the world, is a man who has a rain jacket, but doesn’t bring it…”
  • Extra Clothing – Sitting in your tent half naked with your friends playing cards is embarrassing at the least… Bring extra warm cloths to change into if you get caught in a storm.
  • Map and Compass – Bring a map, talk with locals, and have a plan in case a storm roles in. Redundancy is always recommended.
  • A way to make warm drinks – Hot tea is an excellent moral booster and way to ride out the generally short lived storms. I always keep a small backpacking stove, fuel and metal cup in my car for this reason.
  • Plan conservatively and do not underestimate these storms – Sometimes gentle, sometimes refreshing, these storms can be life threatening in the wrong circumstances. These storms can move very fast and in mountainous environments can be incredibly unpredictable and intense. I have personally been caught in a storm that left me borderline hypothermic when I reached my car on a sunny July afternoon. It was about 75 degrees and there was not a cloud in the sky when I embarked on a hike on the west side of the La Plata Mountains. I was having lunch at about 11,500 feet and turned around (to look west) and I saw not only one storm rolling in, but another storm pushing itself underneath it… Since my position was susceptible to lightning, I immediately packed up and began heading to a lower elevation with more cover. Fifteen minutes later I came to an opening in the trees, and saw the opposing side of the valley was about to be swallowed by churning clouds and rain. I realized then, that I had about 1 minute to get my compass bearings (as all visual land marks were about to disappear). I dawned my flannel shirt and my rain jacket and headed in the direction of the car. My guess was correct, within 5 minutes, visibility went down to about 30 feet (10 m) and the temperature had dropped ten degrees. Fifteen minutes later I was completely soaked and thanking god I had brought my rain jacket on this “sunny” day hike. Because of the lack of visibility, and the varied terrain, it took me four hours to get back to the car. By that time it was 50 degrees, I was shivering almost uncontrollably and I could barely use my hands to open the car door. I drove away thankful, and after getting a few miles down the dirt road I left the valley where the storm circled ominously. Now out of the valley, the sun was out and it was 75 degrees and sunny again.

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There is also a story of a troop of mountain bikers riding just outside the town of Durango who were caught in a summer monsoon. It got so cold so fast (and they were sorely unprepared for rain) that they panicked and called Search and Rescue on a cell phone. By the time the rescue team showed up, the storm was over and the sun was out again. The rescuers reportedly served the soggy cyclists warm tea and directed them to the nearest exit of the trail system. The bikers rode home safe and sound, yet humbled by the storm and how quickly these monsoons can turn a beautiful day into a borderline life threatening situation.

Be safe and have fun out there,

Alex Pullen

For more information on Monsoons in the Southwest read “An introduction to the North American Monsoon System” courtesy of NOAA, or the Albuquerque Monsoon page –