"Haboob" is an Arabic word referring to a giant dust storm. Unlike a localized event of blowing dust, these clouds of dust can overcome metropolitan areas of millions of people, snarling traffic and closing airports.
Arizona haboobs are unique because they rely on thunderstorms in Southern Arizona to start.
Typically, wind slows down as it blows over a long distance because of friction between the ground and the moving air.
But in the haboob setup, gravity is at play.
At 2,400 feet above sea level, Tucson is 1,300 feet above Phoenix (see figure 1).
Figure 1: Tucson is 1,300 feet higher in elevation than Phoenix, making gravity an important part of the haboob formation.
Air traveling from Tucson to Phoenix is accelerated, or pushed forward, by gravity as it pulls the air downhill.
Land in Pinal County, located between Tucson and Phoenix, is largely agricultural (see Figure 2). Plowed fields offer thunderstorm wind easy access to loose soil.
Figure 2: Pinal County is dotted with agricultural plots, making loose soil quite readily available.
A thunderstorm must form in Tucson with it's outflow (wind blowing out of the thunderstorm) heading north into Pinal County for a haboob to begin (see Figure 3).
Figure 3: Wind from a thunderstorm in the metro Tucson area heads downslope toward Phoenix.
Wind is accelerated downslope toward Phoenix, all the while collecting loose soil and sand as it blows over Pinal County.
In a matter of just a couple of hours, zero visibility conditions rush into Phoenix, shutting down transportation and forcing people to rush inside for cover.
Chances of haboobs in 2012 are quite high since Arizona is still in a severe to extreme drought. Droughts result in even more available soil for a haboob to feed on.
If you're wondering, here are other words that are Arabic in the English language. And, the term has been used for decades to describe these gargantuan dust storms.
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