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Monsoon Thunderstorm Season

What’s a Monsoon Thunderstorm?

Arizona’s Monsoon Thunderstorm season is a local part of the North American Monsoon; which occurs over the Mexican states of Sinaloa, Durango, Sonora, & Chihuahua, as well as across the Southwestern United States. Our Monsoon Thunderstorm season in Arizona is experienced as a substantial increase in rainfall from an extremely dry June to a rainy July. These Summer rains typically last until mid-September, when a drier climate is reestablished over the region.

Here is an illustration of a Monsoon Thunderstorm’s anatomy:
Anatomy of a Monsoon Thunderstorm
Click on the image to view the full size image.

The North American Monsoon shares most of the basic characteristics of its counterpart in India. Intense solar heating warms up the during early Summer, causing a shift in wind patterns in Mexico and the Southwestern USA. As this occurs, the flow of prevailing winds start to bring moist ocean areas into dry land areas. The monsoon thunderstorms begin in late May to early June in Southern Mexico and quickly spreads along the Western slopes of the Sierra Madre Occidental, reaching Arizona and New Mexico in early July.

Most of the low-level moisture comes from the Gulf of California and Eastern Pacific. The Gulf of California, a narrow body of water surrounded by mountains, is particularly important for the transportation of moisture into Arizona and Sonora. Upper level moisture is also transported into the region. This upper level moisture mostly comes from the Gulf of Mexico. Evaporation and plant transpiration can add additional moisture to the atmosphere, which will then flow into Arizona. This moisture is available once the forests of the Sierra Madre Occidental green up from the initial monsoon thunderstorm rains. Finally, if the Southern Plains of the USA are unusually wet and green during the early Summer months (June/July), that area can also serve as a source of moisture.

Palo Verde tree damaged by strong monsoon thunderstorm winds

As seen above, the aftermath of a monsoon thunderstorm can leave behind lots of damage, especially to trees. Trees tend to suffer from damaged limbs, branches, and sometimes they’re uprooted and knocked over by the powerful thunderstorm winds. Some damage can compound when damaged parts/trees are moved around by the winds across the other landscape plants. For more information on how to reduce your landscape’s risk of storm damage, please view our Storm Mitigation article.

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