The strongest tornadoes come from the kind of long-lasting, especially fierce thunderstorms known as supercells. As the name implies, these are super thunderstorms with more than their share of potential danger.
In addition to tornadoes, supercells can produce large hail and downbursts. Some bring heavy rain while others are relatively dry. Supercells are most common on the Plains, in the Southeast and across the Midwest, but do occur elsewhere. Not all tornadoes come from supercells, but the strongest twisters usually have a supercell as a 
parent. This past Sunday evening, there were reports from Trigg County of a tornado. But there was no big thunderstorm and no severe weather in the area.
At first glance, even the radar failed to indicate anything that would lead an observer to believe there was a tornado. But a couple of photos from different sources and a short video proved there was something there. One photo and the video was taken by Robin Stevens, a reporter with WKDZ/WHVO Radio.
While we are all familiar with a tornado, few people realize that there are other types of funnels that are usually harmless. But conditions have to be just right to see them. I am talking about cold air funnels. A cold air funnel is a funnel cloud that does not develop in a typical severe weather environment. These funnels tend to form when there is large slow moving low pressure system in the upper atmosphere, similar to the one over the area this past Sunday evening.
Cold air funnels over the Hopkinsville Mall
These cyclonic (counterclockwise) systems generate a lot of vorticity (spin) that enables the funnels to form. Cold air funnels form beneath showers or weak thunderstorms when the air aloft is especially cold. The funnels are most common in the fall and spring when the sun is able to heat up the lower levels of the atmosphere, causing convection to bubble up and form showers, but temperatures around 15,000 to 20,000 feet above the ground are quite cold.
Cold air funnels are usually harmless, but on rare occasions they can touch down and cause EF-0 level (winds up to 85 mph) tornado damage. Normally, the National Weather Service doesn’t issue Tornado Warnings for cold air funnels since it is so rare for them to make it all the way to the ground and become a tornado. They are also difficult to detect on radar since they are very weak. Spotter and public reports are essential when cold air funnels are in the area.
The NWS will usually issue a Special Weather Statement when cold air funnels have been reported.
Of course, a Tornado Warning will still be issued if it is felt that a funnel will touch down. Like waterspouts, cold-air funnels also form beneath cumulus congestus clouds, rather than thunderstorms. The cold air above the warmer ground creates instability that grows the fair weather cumulus. Small-scale wind shear forms the funnels along narrow boundaries on the edges of the clouds, much like gustnadoes.
So, technically, they could be called "gust funnels" because they are like gustnadoes that seldom reach the ground. These funnels are weak and short-lived and usually do not touch down. Those that do reach the ground become weak tornadoes and that is the big difference…they must touch the ground to be called a tornado. Feel free to leave a comment and please hit the “Like” button at the bottom of this post.
