Since there has been some speculation that a gustnado may have developed along the gust front as it struck the Indiana State Fair causing the stage collapse and mass casualty incident, I figured I would take time to post a weather wise blog explaining what gustnadoes are!
While there are some theories that a gustnado may have struck the Sugarland stage at the Indiana State Fair causing the stage collapse, that is neither here nor there as far as this blog entry is concerned. I will tell you however that there were several documented gustnadoes across Central and Western Indiana on Saturday Evening, August 13th, 2011.
A gustnado is a specific type of a short-lived, low-level rotating cloud that can form in a severe thunderstorm. Gustnadoes form due to non-tornadic cyclonic features in the downdraft from the gust front of a strong thunderstorm, especially one which has become outflow dominated. While they often look similar, gustnadoes have very little in common to their big brother, the tornado. Gustnadoes are outflow dominated and often form along gust fronts, while tornadoes form from a rotating supercell and mesocyclone.
One of the key differences and easiest ways to determine a gustnado verses a tornado is that gustnadoes are often not attached to any cloud structure. Tornadoes on the other hand extend down from a rotating wall cloud, a cloud feature that often develops in a supercell thunderstorm. Gustnadoes, while not true tornadoes, can become quite wide and can even be long lived. Gustnadoes should be considered dangerous as they often produce winds in excess of 60 to 70 mph. Gustnadoes have and can do damage.
The picture above is a rotating supercell and associated wall cloud. Wall clouds often have that circular and lowered look and typically rotate, some times quite violently. Most tornadoes develop from wall clouds and supercell type thunderstorms.
The picture above was taken by SWAT Chasers outside of O’Neill, Nebraska on May 30th. The storms that day quickly became outflow dominant and the storms produced numerous gustnadoes all across Central Nebraska. Some of the gustnadoes became quite wide including one we chased which was over 1/2 mile wide. The picture above shows that the rotating column of air, dirt and debris was clearly a gustnado as it was not attached to any wall cloud or lowered cloud base. This particular gustnado occurred on a gust front that surged out ahead of a supercell. What was rare about this particular incident was that to the East of our location, a large gustnado was swirling on the ground. To our West under the actual mesocylone, a tornado briefly touched down under the wall cloud in an open field.
Gustnadoes are often confused and interpreted to be tornadoes by the public and even law enforcement and public safety officials. As stated above, the simplest way to tell a gustnado from a tornado is to check and see if there is a connection to a rotating cloud base. If there is, it is a tornado. If there is not, it is likely a gustnado. If you see a gustnado approaching, you should seek shelter as they can produce strong winds and cause damage.
I hope this blog gave you a little bit of a better understanding of gustnadoes so that when us weather people use the term in the future, you will have a better idea what we are talking about!
Thanks for reading!
P.S. Don’t forget that you can book your storm chase tour with SWATChasers for the 2012 storm chase season! We are offering week long tours that will offer guests a chance to see the incredible Great Plains, Severe Thunderstorms and hopefully tornadoes! You can check out our tour schedule and find more information at SWATTours.com