DALLAS (AP) — Texas and Oklahoma braced for heavy snow and ice that could make roadways treacherous Friday in what forecasters predict will be some of the initial effects of a huge, dayslong winter storm threatening catastrophic damage, extensive power outages and bitterly cold weather to the eastern two-thirds of the U.S.

In the Houston area, a utility company had 3,300 employees ready to work the winter storm, while Oklahoma’s Department of Transportation pretreated highways and interstates with salt brine. Freezing rain and sleet were also expected in New Mexico as early as Friday.

The massive storm system is expected to bring a crippling ice storm from Texas through parts of the South, potentially around a foot (30 centimeters) of snow from Oklahoma through Washington, D.C., New York and Boston, and then a final punch of bitterly cold air that could drop wind chills to minus 50 degrees Fahrenheit (minus 46 Celsius) in parts of Minnesota and North Dakota.

Forecasters are warning the damage, especially in areas pounded by ice, could rival a hurricane. About 160 million people were under winter storm or cold weather watches or warnings — and in many places both.

Cold air streaming down from Canada caused Chicago Public Schools and Des Moines Public Schools in Iowa to cancel classes Friday. Wind chills predicted to be as low as minus 35 degrees Fahrenheit (minus 37 Celsius) could cause frostbite within 10 minutes, making it too dangerous to walk to school or wait for the bus.

The cold punch coming after means it will take a while to thaw out, an especially dangerous prospect in places where ice and snow weighs down tree branches and power lines and cuts electricity, perhaps for days. Roads and sidewalks could remain icy well into next week.

Freezing temperatures are expected all the way to Florida, forecasters said. A severe cold snap five years ago took down much of the power grid in Texas, leaving millions without power for days and resulting in hundreds of deaths. Gov. Greg Abbott said Thursday that won’t happen again, saying the power system “has never been stronger.”

Winter storms can be notoriously tricky to forecast, with forecasters saying the places with the worst weather can’t be pinned down until the event starts.

Governors in Georgia and Mississippi have declared states of emergency, and local authorities are urging citizens to be prepared for significant weather impacts.

By Thursday, airlines had canceled hundreds of flights scheduled for Friday and Saturday, including at airports in Dallas, Atlanta, Oklahoma City and Tulsa, Oklahoma.