From CNBC:

Over 2,000 U.S. flights were canceled on Friday due to winter weather and the grounding of Boeing 737 Max 9 planes, causing more than 4,500 delays, with major disruptions in Chicago and Detroit, where 40% and 20% of flights were canceled or delayed, respectively. Southwest Airlines and United Airlines were particularly affected, and Alaska Airlines canceled all Max 9 flights through Sunday. The FAA grounded the Max 9s after a door plug blew off an Alaska Airlines flight, leading to ongoing inspections and disruptions for United and Alaska Airlines, the only U.S. carriers with the aircraft.



Read more: Flights canceled, delayed as weather, Max 9 grounding disrupt travel