At least 18 dead in storms in central USA: Live updates

The National Weather Service rates the strength of tornadoes using the Enhanced Fujita Scale (EF), which ranks tornadoes on a scale of 0 to 5 based on the amount of damage and wind speed.

These tornadoes are the least destructive and typically break off tree limbs, damage traffic signs, and knock down small trees with shallow roots.

With wind speeds similar to weak hurricanes, these tornadoes can knock moving cars off their tracks, knock mobile homes off their foundations, and tear off roofs.

These tornadoes cause significant damage, can snap or uproot trees, destroy mobile homes, and completely tear roofs off houses.

They can also pick up small objects and turn them into dangerous projectiles.

These tornadoes cause severe damage, uprooting almost all trees in their path, overturning large vehicles such as trains and buses, and causing significant damage to buildings.

Less than 5% of all tornadoes are rated EF3 or higher.

These tornadoes can have devastating effects as they easily destroy homes, overturn cars, and topple large trees.

These monsters cause utter devastation and destroy almost everything in their path.

They are rare; according to the Storm Prediction Center, only 59 such storms have been recorded in the United States since 1950.