Airlines across America have been forced to cancel around 9,000 flights as the country continues to be hit by Arctic weather conditions. US carriers cancelled more than 4,400 flights on Monday, according to FlightAware; that's in addition to a further 4,100 cancelled on Sunday. One of the most affected airports, Chicago O'Hare, saw 1,600 cancellations – over half its daily flights. United Airlines was one of the airlines most affected, as was Southwest, which is the busiest airline at Chicago Midway. JetBlue Airways suspended all flights at New York and Boston airports on Monday, mostly due to the weather but also because of new regulations limiting pilot flying times. The cancellations are due to a wave of brutal polar weather that has been swept down by a vortex from the Arctic. Temperatures have plummeted to as low as -36 Celsius with the wind chill bringing it to -60 degrees, threatening frostbite within just 10 minutes of exposure. People have been warned to stay indoors, schools, malls and offices have been closed and some areas have ordered a driving curfew. The freezing weather is estimated to have killed 13 people already.