Monsoon Special 2012: The Arizona monsoon develops

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By Mike Gertzman By Mike Gertzman

PHOENIX -- The snow from winter storms has long since melted. The Valley is dry, winter rains were well below average. For the past several months, the land has been baking under sunshine that can seem relentless. It is the first sign that the giant heat engine we call the North American Monsoon is getting fuel.

By the middle of spring, a strong high-pressure system is building to the east of Arizona. Winds begin to spin clockwise around that high, drawing moisture from the Gulf of California and the Gulf of Mexico. In the Valley, the first monsoon storms usually arrive around July 4. But by then, the season is already in full swing in the mountains.

The Arizona Monsoon begins officially on June 15 and runs through Sept. 30.

Monsoon storms usually come and go fairly quickly. The average lifespan is less than 30 minutes. But the rain, wind and lightning can become dangerous in an instant.

In Arizona, we average more than 500,000 cloud-to-ground lightning strikes. Some of that lightning strikes homes and power poles, and sometimes the lightning can injure and kill people.

We also have flash flooding, which is one of the leading causes of weather-related deaths.

Microbursts are numerous during the summer thunderstorm season with rain and wind that can swamp your neighborhood in moments, knocking down everything in their path.

So you'd think something this impressive would be rather dependable, but that's not the case. In eight of the past 10 years, Phoenix has received much less rain in the summer. And last year, we received only 60 percent of our average monsoon rainfall.

The Valley gets about one-third of its annual rain from summer storms. But in other areas, like the mountains, the rainfall totals are much more significant.

The town of Greer in the White Mountains leads our Top 5 Monsoon list with nearly 11 inches of summer rain. Nogales and Alpine are close behind at 10 inches while Douglas and Tombstone, in Cochise County, round out the tally.

While the rain benefits more than 10 million people in the U.S. and Mexico, the monsoon can also be dangerous with dust storms and wind gusts over 100 mph.