Monsoon Season

     A monsoon in Arizona?  Yes, indeed.  The term monsoon was originally defined for the Indian subcontinent.  It is actually a wind shift which brings precipitation.  The Arizona Monsoon (some call it the summer thunderstorm season) is part of the larger Mexican Monsoon which occurs throughout the southwest area of the continent from Mexico to as far north as Wyoming.

     Two things happen to bring on our monsoon.  Heat builds in this area in April, May and June (with temps well over 100 F), and an upper level high pressure system (Bermuda High) moves north from winter to summer.  These two events cause the wind to shift from a west or northwest direction to a south or southwest direction bringing tropical moisture from the Gulf of Mexico and the Gulf of California and with it humidity, clouds and rain.

Monsoon Thunderstorm
      The surface heating and strong moisture influx create powerful thunderstorms.  In Arizona we generally get the thunderstorms from July to September.  These are brief downpours, but they flow on dry, hard-packed ground which causes flash flooding.  We get an average of 2.65 inches of rain for all of July, August and September.  Not much considering other areas of the country.  But this is the desert.  We get about 8 inches of rain a year.

Arizona Dust Storm July 5, 2011
       Sometimes, with these powerful thunderstorms, come dust storms.  You might have seen the photos of the two monster dust storms (or haboobs as meteorologists call them) that we have had in Arizona this month.  These dust storms are caused by strong winds flowing downward and outward from thunderstorms, kicking up dust in the dry desert areas.  The dust storm we had on July 5 was 5,000 feet high (1500m) and 100 miles (160 km) wide.  Anything outdoors - furniture, cars, uncovered pools - was covered in dust.  We only got a brief shower out of that storm, the first rain we've seen since March.  That's why xeriscaping ( dry or water efficient landscaping) is common and popular here.


  1. Thank you for a fine explanation, in words and pictures, of such an exotic phenomenon (exotic for Easterners like me).

  2. Didn't know you have monsoons in that part of the world. Here in India, there is much anticipation for the monsoons. The farmers depend heavily on the monsoons for a good harvest. A bad monsoon can mean severe losses and a crisis for them. And a good monsoon means celebrations. For city folk, monsoons mean a respite from the heat, but it also means waterlogged roads and plenty of commuting hassle.
    Can't imagine such powerful dust storms. I've never seen anything like that. 5000 ft of dust!!! Really hard to imagine. Thanks for the picture.

  3. Lee

    I never knew about the monsoon season and dust storms until we moved here. I am awed by the dust storms.

  4. Anita

    I have seen photos of the waterlogged streets during your monsoon season. Until we moved here, I never saw a dust storm either. When you see it coming toward you, it is frightening. You need to seek shelter or the dust will be in your eyes, nose and lungs because of the force with which it blows, usually 50 to 60 mph.

  5. Interesting post. I had seen the photos of the recent dust storms, very scary looking.

  6. Sherry

    These dust storms are scary when coming toward you. And they are dangerous if you are driving as visibility can be reduced to almost zero.