Fast, wet and furious: How the North American monsoon floods the California desert



Colin McGorty-Weir has been helping his family clear out their backyard pool, which is still full of mud and debris that got washed away during a July monsoon in Twentynine Palms.(Gina Ferazzi/Los Angeles Times)

By Ned Kleiner
Aug. 17, 2024 3 AM PT

In the middle of summer, most Southern Californians would be surprised to see more than a handful of clouds in the sky (unless you count clouds of wildfire smoke). But on July 14 in Twentynine Palms, a rapidly developed thunderstorm dropped about 1.88 inches of rain in a couple hours — an overwhelming amount by historical standards for a town that typically gets less than 4 inches in an entire year.

The water rushed along streets and highways, picking up cars and driving debris to damage homes and businesses. Then, while residents were still taking stock of the destruction, nine days later the area was under a flash flood warning again as another thunderstorm moved through.

So why does the Mojave Desert — obviously an extremely arid place — receive all this summer rain while Los Angeles, less than 150 miles away, gets none?

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This changeover is the result of a phenomenon called the North American monsoon, which was responsible for the deluge in Twentynine Palms. While it is less well-known than its South Asian counterpart, the North American monsoon plays an important role in the climate of the Four Corners states, bringing crucial moisture to areas that would otherwise be bone dry, but also at times leading to damaging flooding.

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