What are the signs of a tornado? How do you know when a tornado is forming or approaching? Here are 10 signs that a tornado may be imminent: (UPDATED) 1. The Cloud Base is actually rotating (EVEN IF SLOWLY). Look at the bottom of the cloud base which normally would just be gliding along. 2. A Wall Cloud, a large lowering cloud formation. Look for a lowering of the storm cloud base to what is called a wall cloud. This is a potential tornado sign. 3. Whirling dust debris above the ground (similar to a ‘dust devil’ but bigger).
Original source: 10 Tornado Signs – How To Know If A Tornado Is Coming