Arizona Monsoon Season

Stay Safe During Spectacular Arizona Summer Thunderstorms

If you're a first time visitor or recently moved to Arizona, you may be perplexed by all the summer weather watching.

But spend any time in Arizona's 100°F+ summer and you'll know why we all so eagerly wait for the Arizona monsoon season.

What Is a Monsoon?

Technically, a monsoon is nothing more than a shift in wind direction.

But that simple definition doesn't do justice to the spectacular Arizona summer monsoon season.

Every year - sometime between mid-June and mid-July - the sunny, hot weather in Arizona begins to change as the regional high pressure zone that sits east of Arizona shifts north.

This shift lets prevailing winds, which come from the west most of the year, change direction and flow from the south and southeast.

Known as the Mexican monsoon, this seasonal shift of winds brings tropical moisture from the Sea of Cortez and the Gulf of Mexico into Arizona.

When this moist Mexican air collides with Arizona's desert heat, monsoon thunderstorms are born.

Monsoon thunderstorms are one of the most spectacular and thrilling of nature's displays.

Desert dwellers yearn for the crack of thunder, the brilliant flashes of lightning and the deafening downpour of rain that cools the sweltering desert heat and makes the creosote bushes release their aromatic, herbal fragrance - if only for a few hours.

Most monsoon thunderstorms develop in the late afternoon because that's when heat rises.

When winds push against Arizona's mountain ranges, that air has nowhere to go but up.

That's why storms often start above the mountain ranges first.

Monsoon Season Safety Tips

Read the monsoon safety tips below before going outside or traveling during the monsoon season.

Plan Ahead Before the Storm

• Before going on an outing, listen to the weather reports on radio and TV. The National Weather Service issues Arizona weather watches and warnings via radio and TV.
• A severe thunderstorm warning means that life-threatening storms with winds of at least 60 miles per hour or flash flooding are about to occur or have been reported.
• Have an emergency kit ready in your house and car including first aid items, water, ready-to-eat food, battery-powered radio and flashlights with extra batteries. Do not use candles or oil lamps - they are fire hazards.
• When you're outside, regularly scan the skies 360 degrees around you and overhead. There's no mistaking the tall, skyscraper-like cumulonimbus clouds or the darkening sky.
• Listen for thunder. Anytime you hear thunder, get indoors immediately. Postpone outdoor activities until at least a half hour after you hear the last sounds of thunder or see the last flashes of lightning.
• Do not wait for official warnings before you seek shelter. If you feel threatened, don't hesitate to take cover. The National Weather Service provides advance warning of most storms but severe storms can arise undetected - especially when the storms are producing mostly high winds and little to no rain.

When A Storm Begins

Indoors:

• Turn off all unnecessary electrical equipment. Unplug the computer.
• Stay off the phone unless you need to call 911.
• Stay away from all appliances, wiring, metal objects and water.
• Move to an interior room of the building. Stay away from windows and doors.

Outdoors:

• Minimize your lightning risk. In the past, the NWS recommended the 30/30 Rule: if less than 30 seconds pass between the time you see a flash of light and hear the first roll of thunder, immediately seek shelter in the nearest building. However, they now state that the safest course of action is to go indoors as soon as you hear thunder.
• If you're driving when a serious storm begins, the best thing to do is pull over to a safe parking place and wait for the storm to pass. Keep your windows and doors closed. Turn off your lights. Don't touch any metal parts of the vehicle.
• Do not cross flooded washes or roadways. If a wash or roadway is flooded, do not cross it, even if it is not barricaded. Turn around and take an alternate route. Or, wait until the water recedes. The waters generally take an hour or so to drop.

• Remember the Arizona "Stupid Motorist" Law: a motorist who drives onto a flooded public road or highway, or a wash that is barricaded due to flooding is liable for the costs of any emergency response required to rescue the driver, any passengers and for removal of the inoperable vehicle. Don't park your car under a tree. High winds can break branches and topple even the sturdiest tree.
• If electrical lines fall on your vehicle, stay inside until emergency crews give the o.k. to come out.
• If you must continue driving, drive slower. Leave plenty of room between you and the next vehicle. Obey all caution signs.
• Slow down when you drive through standing water. Even small amounts can cause your vehicle to hydroplane and lose control.
• Be very cautious at night. It's much harder to detect flooded areas in the dark.

Whether you're an Arizona vacationer or a resident, you need to be prepared for the high winds, lightning and rain that are trademarks of Arizona's monsoon season. Be safe and enjoy the beauty of Arizona all year round.

Source: Arizona Vacation Planner, National Weather Service, Department of Geography-Arizona State University, National Oceanographic and Atmospheric Administration, Desert Research Institute