Over 4,000 flights were cancelled and more than 11,000 were delayed on Sunday following disruptions in air travel due to surge of the COVID-19 Omicron variant and adverse weather conditions. As per tracking website FlightAware.com, 2,400 flights departing from or within the US were cancelled. FlightAware also noted that SkyWest and SouthWest airlines recorded the most number of cancellations.