A tornado warning is issued when a tornado has been sighted or indicated by weather radar. If a tornado warning is issued for your area and the sky becomes threatening, move to your pre-designated place of safety. Turn on a battery-powered radio and wait for further instructions. Dark, often greenish sky. Look for signs of debris below the visible funnel.
Some tornadoes are clearly visible, while others are obscured by rain or nearby low-hanging clouds.
Before a tornado hits, the wind may die down, and the air may become very still. An approaching cloud of debris can mark the location of a tornado, even if a funnel is not visible. Tornadoes generally occur near the trailing edge of a thunderstorm. It is not uncommon to see clear, sunlit skies behind a tornado. A mobile home can overturn very easily, even if precautions have been taken to tie down the unit.