The North American Monsoon

Monsoon season is a summer meteorological event throughout the American Southwest. Arizona, New Mexico, Colorado, and Utah are usually the focus. Occasionally, California, Nevada, and Texas are included.

Contrary to popular belief, monsoon does not mean storm. Monsoon comes from the Arabic word “mausim,” or season.

Monsoon storms are an important source of water in the Southwest.  Approximately 40 to 50 percent of the annual precipitation falls during the June 15 to September 30 monsoon season, according to the National Weather Service.

Winds in Arizona usually flow from the West, ensuring dry conditions. But during the monsoon season, winds shift to the South, bringing low-level moisture from the Gulf of California and triggering summer storms. Moisture can also move into Arizona from the eastern Pacific, the Gulf of Mexico, or even from the Sierra Madre Occidental forests in Mexico.

When the dew point (the temperature when condensation occurs) is around 55 degrees or higher, there is enough water to support thunderstorms. Combined with daytime surface heating (ideally 105 degrees) that causes the warm, moist air to rise, storms can form.

These storms are often short-lived, lasting less than an hour. Normally, downdrafts are near the leading edge of the thunderstorm cell. These descending downdrafts often hit the ground and are forced out ahead of the storm, creating a gust front.

In the Arizona desert, gust fronts can pick up and transport large amounts of dust and sand, creating a wall-like structure that moves ahead of the thunderstorm. The term haboob refers to this type of dust storm formed by a gust front.

An approaching small haboob in Texas.

The Shot

Our intrepid group of monsoon thunderstorm chasers renamed our August tour the Nonsoon tour. Dry, scorching hot air with daytime temperatures up to 115 degrees prevented any moisture from reaching the Tucson, Arizona area.

On the second-to-last day of our tour on August 8, the temperature was cooler, and moisture was moving in from the south near the border town of Nogales. We watched several thunderstorms, but they all fizzled out without any significant rain or lightning.

As daylight faded, a beautiful storm just over the border in Mexico began dumping rain and producing lightning bolts. Today’s single image compensated for the prior five days of severely clear and deadly hot non-photogenic days.

Thanks for looking,

Chuck Derus Zenfolio | Chuck Derus