* Blizzard conditions from Arkansas to S.Illinois expected
* Snow expected to target Great Lakes, Northeast Wednesday (Adds power outages, blizzard threats)
WASHINGTON, Dec 25 (Reuters) - A major winter storm brought a rare white Christmas to the southern U.S. plains on Tuesday, contributing to a 21-vehicle pile-up that shut down a major highway in Oklahoma, thousands of power outages and the death of a Texas man.
The storm system surging east from Kansas and the Texas Panhandle included tornados and severe thunderstorms along its southern fringe, from southeastern Texas to Alabama, the National Weather Service said.
The service reported a tornado warning for the Mobile, Alabama area late Tuesday afternoon.
CenterPoint Energy reported more than 20,000 customers without power in the Houston area Tuesday afternoon.
The storm is expected to expected to evolve into a blizzard from Arkansas to southern Illinois Tuesday night, with snowfall of up to a foot in some areas, according to Accuweather.com.
Accuweather.com senior meteorologist Kristina Pydynowski warned on the website that travel will be "extremely treacherous, if not impossible, as the snow clogs roads, such as interstates 24, 55 and 57, and the blowing snow severely lowers visibility."
The snowstorm will shift Wednesday to the eastern Great Lakes and northeast, she said.
Southern Indiana is under a blizzard warning starting early Wednesday morning, according to National Weather Service meteorologist Crystal Pettet. Indianapolis could see its biggest snowfall in four years, with a possibility of 10-12 inches of snow.
"Conditions should be pretty bad in time for rush hour," said Pettet.
A 25-year-old Texas man was killed Tuesday when a tree fell across a road in Harris County, in the Houston metropolitan area, according to Thomas Gilliland of the county's sheriff's office.
A tornado destroyed a building 13 miles (21 km) southeast of Crockett, Texas, and a bank lost a section of its roof, according to Accuweather.com.
Freezing drizzle overnight led to 10 separate collisions on Interstate 40 at Oklahoma City just before 3 a.m., said Trooper Betsy Randolph, a spokeswoman for the Oklahoma Highway Patrol.
The 21-vehicle pile-up included three tractor-trailers and shut down the westbound lanes for about five hours, she said. Twelve people were taken to hospitals, and troopers are checking on the severity of their injuries.
In a rare taste of Christmas snow, Oklahoma City was forecast to get 3 to 6 inches (7.5 to 15 cm) of the white stuff on Tuesday. The city's biggest Christmas snowfall was 6.5 inches (16.2 cm) in 1914, and measurable amounts have been recorded only a handful of times on the date.
The FlightAware website, which tracks flight delays, reported departure delays of 40 minutes from Dallas/Fort Worth International Airport at 5 p.m. local time and 32 minutes from Chicago/O'Hare International Airport.
San Francisco International Airport had delays for inbound flights of over an hour due to low clouds.
Ahead of the storm's path, parts of eastern West Virginia are under a winter storm warning. Ice accumulations of up to half an inch (1.25 cm) are expected in higher elevations, the National Weather Service said. (Reporting by Ian Simpson and Mary Wisniewski; Editing by Sandra Maler and Todd Eastham)