Monday, July 24, 2017

Dust Storms or Haboobs

July 17, 2017 © Thomas J. Kollenborn. All Rights Reserved.

Summer storms in the desert are often called “the monsoons.” These storms bring massive thunderstorms with dust, heavy showers, lightning, dust storms and sometimes devastating winds called “microbursts.” During the summer months most of the storms over central Arizona and the Superstition Wilderness Area result from warm moist air flowing in from the Gulf of Mexico and the Sea of Cortez (Gulf of California). This warm moist air moves across Texas, New Mexico and Mexico. Mountains force this warm moist air upward forming clouds filled with moisture, sometimes saturated to the maximum. These clouds release their moisture as they rise and cool. This is known as orographic lift. The massive anvil-shaped thunderheads that form over Superstition Mountain from July to September are normally formed by two methods: orographic lift and convectional activity. The convectional storm clouds result from rapidly rising and expanding warm moist air and falling cold moist air. This uneven heating of the Earth’s surface is caused by the open cloud pattern in the atmosphere.

Lightning can be caused by the attraction of unlike electrical charges within a thunderhead cell. The rapid movement of ice and water molecules going up and down in a thunderhead cell creates friction that results in an enormous amount of energy in the form of static electricity being produced. A single lightning discharge can produce about 30 million volts at 125,000 amperes. This discharge can occur in less than 1/10 of a second. The results of a lightning strike can be horrific. Never make yourself a target for a lightning strike by standing in an open high area or by a natural lightning rod such as a lone tree on a ridge.

The rapid rising and falling of warm and cold moist air also can create violent bursts of energy. This type of activity results in microbursts, both small and large. Small microbursts can develop winds momentarily up to 200 mph. They also can create winds across wide areas up 80 mph. These are the winds prior to precipitation that can create huge dust storms. These dust storms can momentarily be 100 miles wide, over a mile high and capable of moving tons of desert fines (dust). These storms in Egypt and the Middle East are known as “haboobs” as they roar out of the desert. Since the late 1960s this Middle East name has been attached to Arizona dust storms. Some of these dust storms are enormous and extremely dangerous for transportation.

What is the cause of these dangerous dust storms? One of the most recent and spectacular dust storms occurred on Tuesday, July 7, 2011, and was certainly one of the largest ever experienced by this state. These dust storms appear to be far more severe in recent years. A lot of the Sonoran Desert in Central Arizona had been disturbed for housing pad development on thousands of acres, and then the housing boom died. Now this land sets barren and undeveloped. What little vegetation that covered the desert before preparation for development has been removed. Also unpaved roads and the irresponsible use of ATV and other vehicles off road contribute to the problem. All of this certainly plays a part in this problem of dust storms blowing toward the Salt River Valley from Central Arizona. Yes, there are many other factors to include into this equation, including agriculture, arid condition and uncontrolled growth.

The monsoon storms are associated with very dangerous factors we should all be aware of. These factors include dust storms, high winds, lightning, and flash floods. I have mentioned the other factors in previous columns. If you are caught in a dust storm, use common sense to survive. Get as far as you can off the highway right-of-way, park your vehicle and turn off your lights. Don’t keep your foot on the brake pedal. There are still those who drive in dust and fog at very unreasonable rates of speed, endangering themselves and others. If they see your brake lights, they might drive right off the highway and into your vehicle.

Our desert is being disturbed more and more each year, and the dust storms will probably become more prominent, dangerous and severe. If we are not careful we will be looking like Oklahoma during the “Dust Bowl” of the 1930’s. Oklahoma’s “Dust Bowl” was caused by drought, primarily during the 1930’s. There has been an effort by the cities, state, and counties to suppress the problem with some dust control methods such as paving dirt roads and trying to limit the number of acres of land for vegetation removal for development.

These methods only help, however, during periods of drought. Dust storms are part of living in the Southwest deserts.