Phoenix Dust Storm a "100-Year Event"
By By Heather Buchman, Meteorologist
July 11, 2011, 3:04:46 AM EDT
The photos and video that have come pouring out from the dust storm that hit Phoenix, Ariz., Tuesday have been simply awe-striking.
"Very large and historic" are the words the National Weather Service Forecast Office in Phoenix has used to describe this dust storm that brought widespread reports of near zero visibility and wind gusts greater than 50 mph.
The dust storm was estimated to reach a peak height of at least 5,000 to 6,000 (about a mile) with an aerial coverage on the leading edge stretching nearly 100 miles, according to the National Weather Service. The storm traveled at least 150 miles, much farther than the average 25 to 50 miles that dust storms typically travel.
Ken Waters, Warning Coordination Meteorologist for the National Weather Service Forecast Office in Phoenix, said that the cluster of thunderstorms that spawned the Phoenix storm actually created multiple dust storms, one of which traveled all the way west across Arizona and into Southern California (about 200 miles).
A path of dust and debris was left throughout the Phoenix area. Roughly 10,000 customers lost power. The Phoenix Sky Harbor International Airport had to close for almost an hour late Tuesday with delays spilling over into Wednesday.
The leftover dust is creating health concerns for people with asthma and other respiratory conditions.
These dust storms are common in the southwestern U.S. during the summer, which is the region's monsoon season. During the monsoon, an overall shift in winds across the Southwest draw in tropical moisture, resulting in a significant increase in thunderstorm activity and rainfall.
Thunderstorms that develop can produce strong downdrafts, or "downbursts", which are powerful winds that blast downward and outward from the thunderstorms.
When this happens, dry, loose sand on the desert floors can get kicked up, creating a wall of dust that travels outward, spanning a much larger area than the thunderstorm itself.
Dust storms that develop in this way are also called haboobs. They can happen in desert regions across the world.
Because it has been so dry across the Southwest this spring and early summer, it didn't take much wind to kick up a great deal of dust.
"Rain with these summer thunderstorms is typically spotty enough that there is usually somewhere on the desert floor that the ground is dry enough for the thunderstorm to kick up dust before the rain moves in," explained AccuWeather.com Senior Meteorologist Jim Andrews.
"The dust typically covers a much greater area than the rain," Andrews added, "and the thunderstorm may never get to the places where the dust is."
The Phoenix area only received up to several hundredths of an inch of rain when the thunderstorms moved through late Tuesday afternoon and evening.
The thunderstorms first erupted over southeastern Arizona, causing flash flooding in Tucson before rolling westward across Arizona and into upper deserts of California.
Andrews pointed out that severe but localized flash flooding broke out in some of the deserts of California and southwestern Arizona, especially along the lower Colorado Valley.
While the rain has caused flash flooding problems in the short run, it is much-needed with large portion of the Southwest in a moderate to exceptional drought. More rain will be needed on a regular basis to help improve the drought situation and lessen the wildfire risk that has been plaguing the region.
Accuweather's Jesse Ferrell has more information and 3-D radar on his blog.
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