Best effect ever!

Post production doesn’t come smarter than this collection of backplate projections from “The Wizard Of Oz”.

To coin one of the comments

“It’s a special-effects muslin sock ‘tornado’ made with fuller’s earth running on a gantry on an MGM sound stage in March 1939”

Yet to me this is one of the creepiest, enduring and realistic impressions of a cyclone. Puts CGI to shame.