Every time we have strong to severe storms I get a handful of reports of funnel clouds or tornadoes. Most of the time this is due to misidentifying low clouds that look very ominous but are non-rotating clouds. This is especially easy to do with strong outflow from storms during really hot and humid days. When strong thunderstorms form on days when the temperatures are in the 90s and there’s lots of humidity. The updrafts take that warm & humid air high into the atmosphere where it cools rapidly. That cool air then becomes very dense and wants to rush back to the surface where it then interacts with the hot and humid surface air. This clash near the surface creates “arcus” or shelf clouds that look pretty awesome. These clouds can have all kinds of movement to them but it’s not often a horizontal rotation you’d see in a funnel cloud or wall cloud.
Here are some shelf clouds I saw last weekend at the Beach. Scary looking and they can lead to straight line wind damage from the outflow.
Roger Hill has put together the Non-Tornado Home page. Which has many examples of clouds that looks like tornadoes but aren’t. The best way to determine if a tornado or funnel cloud is present is to see video and radar data in combination. Check out the page…..there are some great examples in there click on the link below.