What to know about monsoon season and dust storms in the Southwest

You may have seen the big dust storm that rolled across Phoenix on Monday afternoon. You’ve probably also heard us talk about these types of storms that happen across the Southwest during the monsoon season.

So, what exactly is monsoon season, and how does it help produce these big dust storms?

When is Monsoon Season?

Every summer, the Southwest U.S. experiences a seasonal shift in weather known as the North American Monsoon.

The National Weather Service (NWS) officially defines this period as lasting from June 15 through September 30, a standard that’s been in place since 2008.

What Causes the Monsoon?

The monsoon is driven by a seasonal change in the upper-air pattern, resulting in shifts in wind direction. This change pulls moisture from the eastern Pacific Ocean and the Gulf of California into the desert Southwest.

The moisture surge is fueled by a high-pressure system over the Four Corners region, which helps funnel humid air into typically dry areas like Arizona, New Mexico, and parts of Utah, Colorado, Nevada, and far West Texas.

As that moisture combines with intense summer heat, it leads to daily rounds of thunderstorms, especially in the afternoon and evening. Some of these storms can lift broad areas of dust, forming large walls of dust.

What’s a Haboob?

The American Meteorological Society (AMS) defines a haboob as an intense sandstorm or dust storm caused by strong winds, often thunderstorm outflows, that can lift dust as high as 5,000 feet.

These storms create a striking “wall of dust” along the leading edge and can quickly reduce visibility, sometimes lasting from several minutes to a few hours.

How Important Is the Monsoon season?

In cities like Tucson and Phoenix, 40-60% of the annual rainfall can fall during the monsoon season. The potential for dust storms isn’t unusual in this part of the country during the monsoon.