The rankings tornadoes get are based on the damage they do. That damage is used to assess a wind speed to how strong the wind likely was inside the tornado for it to be able to do that kind of damage. Surveyors with the National Weather Service look for specific types of damage then assign the EF-ranking to tornadoes based on those markers.
Weak tornadoes get a ranking of EF-0 or EF-1. This is a strength at which we start to see some trees get toppled over, roofs can be stripped, and windows broken. EF-2 and EF-3 are considered strong tornadoes. This is when large trees are uprooted, not just blown over. Cars can be lifted and tossed and outside walls of homes and structures can be destroyed. You are typically able to stay safe in an interior space on the lowest level of the structure with tornadoes of this intensity. EF-4 and EF-5 tornadoes are considered violent. These can debark trees, sweep homes completely off their foundation, and throw cars up to a mile.
Here's more information on the Enhanced Fujita (EF) tornado ranking scale.
DISCUSSION IDEAS:
Where is the safest place to go during a tornado? Why?
