Over 1,000 flights were canceled in the middle of the country Monday due to winter weather conditions that will continue into Tuesday.

Majority of the cancelations occurred at Dallas Love Field, Dallas-Fort Worth International, Austin Bergstrom International and Houston Bush International airports in Texas. Harry International in Las Vegas as well as Denver International also experienced delays.

A winter storm warning will be in effect for a large portion of Texas, especially the Dallas-Fort Worth area until Wednesday.

“If you must travel, slow down and use extreme caution particularly when approaching bridges and overpasses,” said the Texas warning.

Per CNN, more than half of the 1,100 flights canceled or the 5,000 flights delayed were with Southwest Airlines, which previously came under serious scrutiny this past holiday season for delayed flights and poor customer service.

As recently as Monday morning, CEO Bob Jordan was outlining fixes to prevent a repeat of the airline’s Christmas travel meltdown,” reported CNN. “American Airlines and regional carrier SkyWest also saw numerous delays and cancellations.

Southwest Airlines issued a winter weather waiver on Sunday and had extended waivers by midday Monday to a dozen airports in Texas, Oklahoma, Tennessee, Arkansas and Kentucky. The latest waivers apply to travel from January 30 to February 1.

American Airlines issued a waiver on Sunday for Dallas-Fort Worth International Airport (DFW) that applies to travel from January 29 to February 2.

Delta and United have also issued weather waivers. Their Monday operations were not significantly impacted by cancellations.

The Associated Press reported last week that the U.S. Transportation Department will be investigating if Southwest Airlines “deceived customers by knowingly scheduling more flights in late December than it realistically could handle.” The department said such a practice could be considered a “deceptive practice” under federal law.

“DOT is in the initial phase of a rigorous and comprehensive investigation into Southwest Airlines’ holiday debacle that stranded millions,” the department said.