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The National Weather Service offices in West Texas have received a few reports of tornadoes today. These reports came in from the leading edge of the thunderstorm gust front that brought about all the dust. For those who have taken spotter training classes, you know that tornadoes form in the inflow region of a thunderstorm (the updraft) and not on the leading edge of an outflow boundary. So that begs the question, were there tornadoes today? The answer is NO!

800px-Gustnado

This graphic illustrates today’s situation. You have cool air rushing out and ahead of the thunderstorm. This cool air pushed out about two to four miles ahead of the main rain activity today. When air pushes out ahead of a thunderstorm, we call it a gust front. A gust front marks the leading edge of the cooler, stable air and is usually ahead of the thunderstorm by some distance. Thunderstorms ingest warm, unstable air to produce low-level rotation and potentially tornadoes. When the gust front rushes out ahead of the storm, it cuts off the warm inflow. That practically eliminates the tornado threat.

When the cool, stable air with the gust front interacts with the warm, unstable air ahead of it, there is often some turbulence  A example of this would be when a shelf cloud passes overhead and you’re able to see the turbulent cloud motion. With today’s setup, conditions were marginally favorable for the development of gustnadoes. A gustnado can be described as a dust-devil on steroids. They’re usually weak with winds of 30 to 50 MPH, although they can become as strong as an EF-1 tornado under rare circumstances. While tornadoes are produced by a mesocyclone in a thunderstorm, gustnadoes are associated with the leading edge of the thunderstorm’s outflow.

With West Texas in drought conditions, gustnadoes are more likely to be noticed since they’re able to pick up dust and dirt. While they may have a similar appearance to a tornado, they’re in no way the same animal. I myself have driven through gustnadoes just for the fun of it! Here is the official definition of a gustnado from the National Weather Service.

A slang term for a short-lived, ground-based, shallow, vortex that develops on a gust front associated with either thunderstorms or showers. They may only extend to 30 to 300 feet above the ground with no apparent connection to the convective cloud above. They may be accompanied by rain, but usually are ‘wispy’, or only visible as a debris cloud or dust whirl at or near the ground. Wind speeds can reach 60 to 80 mph, resulting in significant damage, similar to that of a F0 or F1 tornado. However, gustnadoes are not considered to be a tornado, and some cases, it may be difficult to distinguish a gustnado from a tornado. Gustnadoes are not associated with storm-scale rotation (i.e. mesocyclones) that is involved with true tornadoes; they are more likely to be associated visually with a shelf cloud that is found on the forward side of a thunderstorm. – National Weather Service

Here is a public record image of a gustnado. As you can see, it does have a similar appaerance to a tornado. However, it is on the forward-flank of the storm and not in the rear-flank where you would have the thunderstorm’s updraft. Since tornadoes are produced from mesocyclones (fancy word for rotating updraft), this is not a tornado.

Gustnado_in_Jefferson_County,_Kansas_on_April_3,_2011

 

David Reimer

David Reimer

Owner at Texas Storm Chasers LLC
David Reimer

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