How to determine dust devils from tornadoes

Many desert dwellers are used to the sight of swirling dust and sand in an open field on a sunny afternoon, but when is a dust devil no longer a dust devil?

After pictures and video of a vortex near Desert Center began streaming into our newsroom Tuesday afternoon, there was a lot of debate on our social media pages as to whether or not the long tube of dust and sand was actually a tornado.

So what's the difference between the two?

The American Meteorological Society (AMS) defines a dust devil as, "A well-developed dust whirl; a small but vigorouswhirlwind, usually of shortduration, rendered visible bydust, sand, and debris picked up from the ground."

It defines a tornado as, "A rotating column of air, in contact with the surface, pendant from a cloud, and often visible as a and/or circulating debris/dust at the ground."

"Pendant from a cloud" is key here. Tornadoes musthave a parent cloud the updraft extends to. If the vortex extends all the way from the ground to a funnel at the base of the cloud it's a tornado.

Dust devils can exist independently under a storm but by reviewing images, video, and eye witness reports, the National Weather Service in Phoenix was able to determine that the vortex just north of Desert Center did indeed meet the criteria to be designated a tornado. The rotating funnel in the cloud base is obvious in the photos shown above, as well as the strong circulation on the ground.

But wait! Can dust devils become tornadoes? Absolutely! It's possible that the Desert Center tornado was indeed a dust devil first, but we haven't received any reports about its formation so we can't be certain.

Dust devils can become tornadoes when a storm's updraft moves over the the existing ground circulation. The updraft from the storm can draw the dust devil vertically into the base of the cloud, often strengthening the rotation as it does through conservation of angular momentum. You can think of it like a figure skater spinning and gaining speed as they straighten and extend their arms upward. The same can be done in a rotating chair if you quickly bring your extended arms in towards you chest.

The strongest and longest lived tornadoes that occur more often in the Great Plains and the Midwest usually form under a storm with a larger circulation known as a mesocyclone. Unfortunately due to the tornadoes location, the closest radar site in Yuma, Arizona could only detect the storm above 10,000 feet, much higher than where the vortex was spinning.

Since no rotation was detected on radar it is not clear whether this tornado formed under a mesocyclone or another process. Tornadoes that do not form under a mesocyclone are often called landspout tornadoes.

The National Weather Service in Phoenix has given the tornado a rating of EF0, the lowest possible on the Enhanced Fujita scale. EF0's have winds of 65-85 mph and cause minor to no damage. More information can be found here:http://www.wrh.noaa.gov/psr/pns/2015/April/DesertCenter.php