A gap of clearer air that wraps around the rotating part of a supercell, created by the rear-flank downdraft. Many tornadoes form near this notch.
Supercell cross-section. Warm, moist air flows in low on the right and rises in the rotating updraft; the wall cloud and tornado form under it, between the rain-and-hail core and the rear-flank downdraft.
How to spot it
A bright, rain-free notch of sky cutting into the back of the storm near the wall cloud.
On radar
The notch between the hook and the main echo.
Safety
The clear slot may bring very strong winds from the rear-flank downdraft. Do not stand in it.
