50 million people under severe weather alert after California tornadoes, mudslides

More than 50 million people across a large swath of the nation were on alert Thursday for tornados, large hail, damaging winds and flooding after a severe weather outbreak spawned by a "bomb cyclone" in California moved east, leaving a wake of destruction from mudslides, tree-toppling gusts and the largest twister to hit the Los Angeles area in 40 years.

Residents of Texas and Oklahoma and up to Pennsylvania are bracing for large hail, flooding and tornadoes Thursday night.

The wild weather system is the same one that blew in from the Pacific Ocean in Northern California as a "bomb cyclone," packing powerful winds that toppled more than 700 trees in San Francisco and killed at least five people in the Bay Area who were either struck by falling limbs or uprooted trees, officials said.

The storm pummeled the Golden State for two days, flooding farmland in the San Joaquin Valley and generating two confirmed tornadoes in Southern California, one just 10 miles from downtown Los Angeles.

The LA-area twister, the strongest to hit the area since March 1983, was rated an EF1, which is on the lower end of the Enhanced Fujita tornado damage scale, according to the National Weather Service. Yet the 110 mph winds the tornado generated wrecked 17 structures, including 11 that sustained significant damage, according to the National Weather Service.

The ferocious Southern California funnel cloud touched down just after 11 a.m. local time in Montebello, just 10 miles east of downtown Los Angeles, and stayed on the ground for about three minutes, sending debris, including an industrial-size rooftop air conditioning unit, swirling into the air, according to the weather service.

The tornado touched down in an industrial park, completely collapsing the roof of one warehouse, snapping a power pole and uprooting trees, officials said. One person suffered minor injuries as a result of the tornado activity, according to the Montebello Fire Department.

"This was crazy. I mean we're used to earthquakes, but not tornados," Mike Turner, who was working in one of the damaged warehouses, told ABC Los Angeles station KABC.

Turner said the twister ripped off an estimated 5,000 square feet of the factory's roof.

"It got real loud. Like I've never heard before and for about 30 seconds to a minute," Turner said. "Then we kind of all were in the office and then after it died down, we went outside, and there was debris everywhere. It was like dust bowl in the factory."

A second tornado, rated an EF0, touched down in Carpinteria in Santa Barbara County, generating 75 mph winds and damaging 25 mobile homes, according to the National Weather Service.

Compared to the South, tornadoes in California are rare. There have been 469 tornadoes in the state since 1950, according to the National Oceanic and Atmospheric Administration. Since records began in 1950, California averages 6.4 tornadoes per year. But in the last 30 years, the state has averaged 10 twisters per year, according to NOAA. Los Angeles County has had the most of any country in the state with 46 since 1950, followed by nearby Orange County with 31. 

The storm system was accompanied by torrential rain throughout the Los Angeles region, triggering a mudslide in San Bernardino County and prompting the rescues of 17 farm animals -- including horses, cows and bulls -- that got stuck in the mud, according to the San Bernardino County Animal Control.

As the menacing storm moves into Texas and Oklahoma Thursday evening, residents are being warned to expect large-size hail and the possibility of more tornadoes forming from Dallas to Oklahoma City and Tulsa. Widespread flooding is expected over the next few days from Oklahoma to Pennsylvania.

A flood watch is in effect for parts of 10 states from the Mississippi River Valley to the Ohio River Valley, where several inches of rain are forecast.

As the storm moves farther east on Friday, a strong threat of tornadoes is expected for parts of Louisiana, Arkansas, Mississippi and Tennessee, officials said. Among the cities bracing for twisters are Jackson, Mississippi; Little Rock, Arkansas; and Memphis, Tennessee.

The severe weather is forecast to bring rain and snow to Chicago, the Great Lakes and Northeast over the weekend. Heavy rain and gusty winds are expected from Washington, D.C., and Philadelphia to New York City and to Boston.