A blast of Arctic air has rolled into the central U.S., fueling a storm that is tying up air traffic and threatening to bring ice and sleet as far south as Texas, where flights are being canceled.

American Airlines Inc. and its regional partner American Eagle have canceled 500 flights at Dallas/Fort Worth International Airport through Friday, according to an email from Andrea Huguely, a company spokeswoman in Fort Worth.

Around the U.S. today, 665 flights have been scrubbed including 278 at Dallas/Fort Worth, 181 at LaGuardia Airport in New York and 61 at Philadelphia International Airport, as of 12:30 p.m. New York time, according to FlightAware, a Houston- based airline tracking service.

Freezing rain is expected to start falling in North Texas tonight, coating roads, trees and power lines with a layer of ice at least 0.25 inch thick, according to the National Weather Service.

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“Ice accumulations will create hazardous travel conditions on area roads, especially on bridges and overpasses,” the weather service said in a winter storm warning for Dallas and Fort Worth. “Ice accumulations may make road surfaces impassable at times through Friday afternoon.”