CORRECTED-UPDATE 1-Blizzard strikes US Midwest, cancelling flights and disrupting presidential campaign

(Corrects spelling of Iowa voter's name in paragraphs 7 and 8 to Schuster, not Shuster)

By Brendan O'Brien and Rich McKay

CHICAGO, Jan 12 (Reuters) - Tens of millions of Americans were in the pathway of dangerous and damaging weather conditions as snowstorms moved across the Northwest and Midwest, flooding threatened the East Coast and potential tornadoes were on tap in the South.

Airlines canceled or delayed more than 5,000 flights across the U.S. on Friday, including planes grounded at Chicago's O'Hare International Airport due to winds and blinding snow. In Iowa, Republican presidential candidates canceled events three days out from the state's caucuses, the first of the state-by-state contests in which parties pick their nominees ahead of this year's general election.

Blizzards arrived in much of the upper Midwest on Friday morning with heavy snows and fierce winds of up to 60 miles per hour (96 kph) that were expected to continue into Saturday, the National Weather Service (NWS) warned.

"This storm system is definitely dangerous," said Zack Taylor, a meteorologist with the NWS's Weather Prediction Center in College Park, Maryland. The service cautioned against unnecessary travel, noting that visibility on some roads in Chicago was less than half a mile.

Taylor warned of risks of frostbite and hypothermia in Iowa, where temperatures for most of the state were forecast to drop below zero degrees Fahrenheit (minus 18 degrees Celsius). The forecast in Des Moines, the state capital, was a low of minus 18 F (minus 28 C). Temperatures for Monday's caucuses, which entail long meetings in churches and school gyms, are expected to be the coldest on record for that political event.

Republican presidential candidate Nikki Haley, a former ambassador and South Carolina governor, canceled all three campaign events planned for Friday, substituting them for phone-in events.

Fred Schuster, 68, braved Friday morning's blizzard to watch Ron DeSantis, Florida's governor, campaign in Ankeny, Iowa.

"I am worried about the weather," Schuster said. "I think it's going to impact how many people attend the caucuses."

Officials canceled a planned rally in Pella, Iowa, for supporters of Donald Trump, who is seeking a second White House term after losing 2020's election.

There were more than 160,000 power outages across five states including Illinois, Texas, Wisconsin, Arkansas and Tennessee, according to the tracking site PowerOutage.us.

By midmorning on Saturday, there could be 3 to 6 inches of snow in downtown Chicago. Throughout Friday, as the snow falls, strong winds could bring whiteout conditions.

Chicago Public Schools remained open while dozens of other districts across the metro region canceled in-person classes for the day.

The snow and wind caused more than 1,500 flights to be canceled or delayed in and out of O'Hare International Airport on Friday morning. Across the U.S., more than 5,000 flights had been canceled or delayed, according to FlightAware.

Milwaukee, Wisconsin, is expected to receive some of the heaviest snow as the blizzard will drop 12 to 18 inches, with wind gusts up to 40 mph through the weekend.

Western New York, including Buffalo, could get more than a foot of snow. But after this system pushes east, "lake-effect" snow could bring several more inches through Monday to the Buffalo area.

Another 13 million people who live near the Atlantic Ocean or large waterways in Virginia north into New England were under the threat of flooding from heavy rains and snows over the past few days.

To the south in Mississippi, some 3 million people were under the threat of tornadoes and severe thunderstorms as the NWS warned that the winds of up to 60 mph could damage roofs and take down trees and power lines.

A winter storm system was also hitting the Pacific Northwest on Friday, and tracking through the Central Rockies with heavy snow that could drop "a couple feet of snow" at the higher elevations over the weekend, Taylor said. (Reporting by Brendan O'Brien in Chicago and Rich McKay in Atlanta; Additional reporting by Tim Reid in Ankeny, Iowa; Nathan Layne in Des Moines, Iowa; and Jonathan Allen in New York Editing by Matthew Lewis)