GOLDEN VALLEY, Minn. — There was severe weather in southern Minnesota on Saturday, but it was a funnel spotted near Alexandria on Sunday that was getting a lot of attention on social media, when it formed without any storms around.
In this case, it was a cold-air funnel. The biggest difference between a cold-air funnel and a traditional tornado is it forms behind the cold front in that shallow layer of cold air; by contrast, a tornado forms ahead or along the front.
All that's needed is a little bit of wind shear to get the spin from the rising air coming off the surface. In Alexandria on Sunday it was about 83 degrees, which was warm enough as the air rises that shear gets it to spin.
The other difference between Sunday's funnel and a traditional tornado is the cloud base it must reach to get the funnel to form is a lot higher. A tornado in a typical thunderstorm is going to form on a cloud base that's a lot lower due to the instability of the atmosphere.
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A cold-air funnel is a bit more stable which is why they're very, very weak and rarely touch the ground. If they do, it's usually an EF-0.
Basically, it's a pretty cool phenomenon, but otherwise harmless.
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