DARRYL WEBB/EAST VALLEY TRIBUNE-AUG,21,2009-Lightning shoots horizontally across the sky behind Chandler's Seton High School chapel Friday night.

The monsoon is set to begin next week.

But where are the signs of the storm season that is scheduled to be here for the next four months?

“Nothing is on the horizon, but it’s still pretty early,” said Mike Bruce, a meteorologist with the National Weather Service.

While there was a normal monsoon last year as 2.48 inches of rain fell, this year’s temperatures leading up to it have been below normal and will be that way for at least another week.

The monsoon is a shifting of winds which happens in the Southwest in the summer. It can bring rainstorms that benefit the area, but can also have the potential to cause a great deal of havoc. The sea surface temperatures of the Pacific Ocean help determine the strength of our monsoon each year, according to the National Weather Service.

The intense heat of Arizona’s deserts can create a drop in air pressure called a thermal low. That air pressure draws moist, cooler air, creating an unstable situation that turns into a thunderstorm. The current pattern looks to repeat itself, with west-to-east wind blowing through Arizona through at least mid-June. This will push dry air into Arizona and prevent the pre-monsoon pattern from forming.

The monsoon can bring minor dust storms to violent thunderstorms and spawn tornadoes in rare instances. Typically, Arizona monsoon storms start with heavy winds sometimes resulting in a visible wall of dust hundreds of feet high moving across the Valley.

The rain from those thunderstorms increases humidity over the land triggering more thunderstorms, and the cycle continues until cooler air arrives in the fall.

Monsoon rains average about two-and-a-half inches or one-third of the Valley’s annual rainfall.

“Beyond the state of the science (of predicting weather), the monsoon is a little more unpredictable,” Bruce said. “Right now, it’s just very sketchy. A wet winter does not mean a wet or dry monsoon and a dry winter does not mean a wet or dry monsoon.”

As three major forest fires are raging throughout the state, the monsoon could be both a good and bad thing: The rain would help douse fires, but the lightning could also start other blazes.

As Valley residents normally see temperatures in the low 100s this month, weather forecasters project this week’s temperatures to remain mostly in the high 90s, with a high of 100 to 102 on Thursday, according to information from the National Weather Service.

Then next week, the temperatures will remain in the 90s, which are lower than normal for this time of year, Bruce said.

• Contact writer: (480) 898-6533 or

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