Cumulus clouds don't so much appear in tornadoes. It is more accurate to say that tornadoes descend from cumulonimbus clouds.
Tornadoes happen in both hemispheres.
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Every state has had at least a few weak tornadoes.
The top five states with the most tornadoes are:TexasOklahomaKansasFloridaNebraska
No part of Arizona is completely free of tornadoes, but they appear to be less common in the western part of the state.
Tornadoes do not always appear black. The apparent color depends on lighting conditions and how much and what color of soil is being lifted. Many tornadoes appear dark because of perspective: the are lit from behind and are essentially silhouetted against the light source. The same tornado may appear lighter if viewed from a different angle. The storms that spawn tornadoes have very thick clouds that often making conditions appear very dark. The clouds themselves may be black. Some tornadoes may be black as they lift large amounts of black soil into the air.
Tornadoes typically appear in regions known as Tornado Alley in the central United States, as well as in other parts of North America, Europe, South Africa, Argentina, Australia, and New Zealand. These regions usually have the right mix of atmospheric conditions for tornado formation, such as warm, moist air colliding with cool, dry air.
All 50 states get tornadoes though they are rare in many of the states.
The U.S. averages about 1200 tornadoes per year.
There were 1692 confirmed tornadoes in the U.S. in 2011.
Tornadoes can form almost anywhere in North America but occur most often on the central plains of the United States.