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Arizona Monsoon

Arizona Monsoon

During the monsoon, or summer thunderstorm season, Arizona experiences more severe weather than many other states. On some occasions, a severe storm may spawn a microburst. More often, high winds, dust and severe downpours resulting in flash floods are common monsoon occurrences.

Beginning in 2008, June 15 is established as the first day of monsoon, and September 30 will be the last day. Now we can be more concerned with monsoon safety and less concerned with definitions.

More About Phoenix Monsoon

Meteorologists still track and report dew points and study monsoon weather patterns

Here are some technical monsoon facts for our area. The facts relate to dew point and the meteorological definition of monsoon and not the date on the calendar.

  • The average starting date of the monsoon in Phoenix is July 7.
  • The average ending date of the monsoon is September 13.
  • The earliest start date for the monsoon was June 16, 1925.
  • The latest start date for the monsoon was July 25, 1987.
  • The average date of the first break in the monsoon is August 16.
  • The average total number of monsoon days (where a monsoon day is considered one with an average dew point of 55 degrees or higher) is 56.
  • The greatest number of monsoon days was 99, recorded in 1984.
  • The fewest number of monsoon days was 27, recorded in 1962.
  • The greatest number of consecutive monsoon days was 72, from June 25 through September 4, 1984. This was also the greatest number of consecutive days with dew points of 60 degrees or higher.
  • In Phoenix, normal rainfall during July, August and September is 2.65 inches.
  • The wettest monsoon occurred in 1984 when we had 9.38 inches of rain.
  • The driest monsoon occurred in 1924 with only 0.35 in


When Is Arizona’s Monsoon?

Up until 2008 Arizona’s monsoon varied from year to year in starting date and duration. The Arizona monsoon officially began after the third consecutive day of dew points above 55 degrees.

On average this occurred around July 7 with the monsoon continuing for the next two months. In 2008 the National Weather Service decided to take the guesswork out ofmonsoon start and end dates. From now on June 15 will be the first day of the monsoon, and September 30 will be the last day. They did this simply to take the focus off whether or not a storm was considered a monsoon storm or not, and have people be more concerned with safety.

What Happens During Monsoon?

Monsoon storms range from minor dust storms to violent thunderstorms. They can even spawn tornadoes, though that is very rare. Typically, Arizona monsoon storms start with heavy winds sometimes resulting in a visible wall of dust hundreds of feet high moving across the Valley. These dust storms are normally accompanied by frequent thunder and lightning often leading to heavy downpours. Monsoon rains average about 2-1/2″, about 1/3 of our yearly rainfall.

Is there Damage During Monsoon Storms?

Serious damage can occur from high winds, or from debris being tossed by those high winds. It is not unusual for trees to be downed, power lines to be damaged, and roof damage to occur.

As you might imagine, homes that are not as sturdy, like some manufactured homes, are more susceptible to wind damage. Power outages for short periods of time are not uncommon.

Monsoon Safety

  1. If you see a sign that says “Do Not Cross When Flooded,”take it seriously. If you are caught in a wash, try to climb out on the roof of your vehicle and wait for help. Use your cell phone, if available, to call 911.
  2. If you’re driving when it’s raining, slow down. Remember that the beginning of rain storms in the area are the most dangerous times since that’s when oils and other automotive fluids are being washed off the roads causing unusually slick conditions.
  3. If your visibility is impeded by heavy rain or blowing dust, most people will reduce their speed, but keep driving straight. Don’t change lanes unless absolutely necessary. Area drivers will often use their emergency blinkers (hazard lights) during the storm because blinking lights are easier to see. If you don’t want to drive in the storm, slowly pull off to the side of the road as far to the right as possible, turn off your car, turn off your lights, and keep your foot off the brake pedal. Otherwise, drivers may come up quickly behind you assuming that you’re still in motion.
  4. To avoid being struck by lightning stay away from open fields, high land, trees, poles, other tall objects, standing bodies of water including swimming pools, and metal objects including golf clubs and lawn chairs

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Be careful this Monsoon season and keep up to date with your local weather station for more information on what to expect.

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