CHICAGO (CBS) — The holiday travel rush is kicking into high gear, but threats of severe weather could put a damper on Thanksgiving plans for many travelers.

The Chicago Department of Aviation said more than 1.6 million passengers will pass through Chicago’s airports this week, with Sunday expected to be the busiest day at both O’Hare and Midway.

As of 9 a.m., despite a rainy start to the day, fewer than 5% of the flights at both O’Hare International Airport and Midway International Airport have been delayed, with those delays averaging less than 15 minutes.

Airlines expect their busiest Thanksgiving ever, but a major storm system moving across the country could be an issue for travelers, including a winter blast of rain and sleet that could disrupt air travel in the Northeast late Tuesday night into Wednesday.

“It’s getting better. The process of what they’re doing has improved, and it’s really good. We went through, and each person that was available was able to assist us right away. We came early to try and avoid all of the stress, and really no stress,” Midway traveler Geraldine Taylor said.

At Midway, the number of travelers is up 1% compared to this time last year. Travelers are advised to show up at the airport early, even if they are enrolled in TSA PreCheck.