Partner Series

{youtube TtJaGoE_8JU}

The second tornado in four days, not including a rare waterspout, touched down in California yesterday.

California isn't exactly Tornado Alley the twister hotspot of the United States with only about five tornadoes per year. But as West Coasters have seen, tornadoes can form at any time and any place, often with little notice. [Related: Twisted Science: Why Tornado Forecasting Is Tough ]

Last Friday (March 18), a storm spawned a waterspout that touched down off Ocean Beach. The same storm created an EF-1 tornado that destroyed a metal building in Santa Rosa, according to the Storm Prediction Center in Norman, Okla. Yesterday an EF-0 tornado briefly touched down near Maxwell, Calif.

California twisters

California is a prime example of how twisters can form under many conditions. Textbook tornadoes form in Tornado Alley in the Great Plains, where warm, moist Gulf of Mexico air collides with cool, northern air, creating the massive storms that spin off tornadoes.

{youtube 22nh5VglqkI}

In California, Friday's tornado was due to instability created along a cold front and channelized winds intense winds blowing in the same direction that generated swirling storms, said Mark Strobin, a meteorologist with the National Weather Service in Monterey, Calif.

Yesterday's tornado in Maxwell was caused by an upper level low-pressure system swinging through behind that cold frontal system, said Tom Dang, a meteorologist with the National Weather Service in Sacramento.

"This is the typical regime for that to happen," Dang told OurAmazingPlanet.

Yet even if this weather pattern were to happen 10 times, a tornado would probably only form once or twice, Dang said. Still, when spring rolls around in the United States, everyone has to be prepared for tornadoes.

Down the alleys

Tornado season began earlier this month, and typically hits its stride from May to June.

Thousands of tornadoes will strike the United States each year, mostly in the hotbed known as Tornado Alley, bordered by the Dakotas to the north, the Gulf Coast to the south, the Rocky Mountains to the west and the Appalachian Mountains to the east.

Southeast of Tornado Alley is Dixie Alley, home to the deadliest tornadoes. In 2010, Mississippi led the nation with three killer tornadoes and 13 tornado related deaths.

Outside the zone

The big tornado alleys may attract all the attention, and the brave storm chasers , but every state even Alaska can have tornadoes. Maine has about two tornadoes each year, and Arizona has three. For the first time, Minnesota led the United States with 113 tornadoes last year.

New Jersey and New Hampshire had one tornado each, last place among states that saw tornadoes in 2010. Of course, tornadoes aren't a purely American weather menace. Touchdowns have been reported on every continent except Antarctica.

Tornadoes don't just form during the day either. Night twisters can be some of the most deadly because tornadoes are hard to see at night and people tend to sleep through warning sirens. Thirty-nine percent of tornado fatalities and 42 percent of killer tornado events occur at night.

Tornadoes can also strike during any time of the year (November is often called the second tornado season ), even during the winter. A tornado hit New York City at night in September last year.

In 2010, 45 people were killed by tornadoes across the United States.
