Answers: Arizona tornadoes
Q: Do tornadoes occur in south-west Arizona, including in the Yuma area?
Chris, Yuma, Ariz.
A: A few tornadoes have occurred in Yuma County in the past, which means that they can occur in the future. Nevertheless, the record shows they are rare and usually weak.
If you go to the National Climatic Data Center’s (NCDC) Storm Events Web page, select “Arizona” with the pull-down menu, and then select “Yuma” county you’ll find a list of “storm events” including tornadoes, dust storms, floods, hail storms, and thunderstorm winds from Jan. 1, 1950 through Feb. 2, 2010. Records of such events before 1950 are spotty at best.
(The NCDC is the National Oceanic and Atmospheric Administration (NOAA) division that keeps and studies weather and climate records for the United States.)
The 196 “storm events” listed include only 11 tornadoes and three “funnel clouds,” which are tornado clouds that didn’t touch the ground. The strongest tornado was an F-2, which hit on Aug. 17, 1959 causing one reported injury and $250,000 in property damage.
“F-2″ means that the tornado’s winds were estimated to be between 113 and 157 mph. By the way, since February 2007 the NWS has been using the Enhanced Fujita Scale. It, like the original Fujita scale gives only estimates of tornado winds.
In general, tornadoes occur when a strong mass of cold air moves into an area dominated by warm air. In addition, tornadoes occur with particular upper-air patterns of winds and temperatures. These conditions are rare in desert climates such as in Arizona.
However, strong thunderstorm winds, which can do as much damage as many tornadoes, occur in Arizona.
Chapter 8, on thunderstorms, of my AMS Weather Book: The Ultimate Guide to America’s Weather explains in words and graphics what causes tornadoes, what conditions are needed, how tornadoes are forecast, and why the tornado damage scale is named for the late Theodore Fujita, who was an important tornado scientist.
While tornadoes are rare in desert climates, dust devils, which look somewhat like tornadoes near the ground, are common. A dust devil, unlike a tornado, is not attached to a cumulus cloud. All tornadoes form in thunderstorms and descend to the ground. A Wikipedia article on dust devils explains what they are, how they form and how they are different from tornadoes.
- Web site of Jeff Alu, the dust devil photographer.