Another 2,044 flights were cancelled Thursday, according to flight tracking service FlightAware, pushing the total for the week above 18,000. The airlines are scratching some flights to keep their systems from getting overwhelmed as they ramp up service at hard-hit airports like Chicago's O'Hare.
In addition, freezing rain and cold temperatures are disrupting service to Houston and Dallas, the site of this Sunday's Super Bowl.
The bulk of canceled flights were in Chicago. O'Hare International Airport reported 1,000 cancellations, according to the Chicago Department of Aviation.
About 578 flights were cancelled as of 12:15 p.m. EST at Houston's Bush Intercontinental and 193 at Dallas Fort Worth Airport. Much of Texas is under a hard freeze warning.
Planes that are flying are seeing mostly clear skies across the country. The Federal Aviation Administration reports no significant delays at any of the major airports.
Chicago is the home base for United. Continental is based in Houston and American is based in Dallas. Cancellations or delays at these airports can ripple across the country because travelers use those cities for connecting flights to other locations.
The latest cancellations added to record tallies this week. Airlines have canceled nearly 18,400 flights since Monday. That's almost double the roughly 10,000 cancellations from the huge post-Christmas blizzard.
It's too soon to assess the impact on the airline's bottom lines. Storms in December sliced $10 million from United Continental's fourth-quarter operating profit of $160 million, and that storm shut down Continental operations at its Newark hub for two days.