We in the Chihuahuan Desert are well aware that an approaching thunderstorm often is heralded by a wall of furiously churning sand and dust accompanied by the banshee howl of all-enveloping wind. Indeed, severe damage by such storms often is by this dry, advance guard rather than by the wind, rain, and hail of the following tempest.
The towering clouds of our monsoon storms are caused by
updrafts—by bubbles of hot air rising through cooler air like giant, hot-air
balloons until, cooling by expansion, their contained moisture condenses out, forming
clouds and then raindrops. Rain, falling through warm air, cools that air and, cool air
being heavier than warm air, this glob of colder air sinks. The surrounding air gets
warmer and warmer as the ground gets nearer and nearer, and the sinking cold air picks
up speed until, slamming into the ground, it spreads out horizontally, picking up
anything loose. Under the right conditions, these sand-carrying winds may reach
hurricane speed—no wonder the alert home owner scurries madly about, slamming
shut windows and doors!
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.