More than 80% of Southwest Airlines' schedule was disrupted in the wake of the massive winter storm that hit the US.

Southwest was responsible for almost three-fourths of the canceled flights in the US. That made the biggest discount carrier an unhappy outlier in the US industry.

Although the airline was fully staffed for the holiday, 23 out of its 25 top airports were affected by the storm.

The airline said in a statement that challenges are impacting customers and employees in a way that is unacceptable. The storm caused daily changes to our flight schedule at a volume and magnitude that still has the tools our teams use to recover the airline operating at capacity

In the midst of a busy holiday, travelers took to social media to vent about the turmoil. Southwest's stock is down 16% this year and is headed for a third straight annual decline.

The storm hit a wide swath of the US and Canada, with record snow totals in the Midwest and Buffalo, New York, where as many as 27 people have been reported dead.

Getting Worse

More than half of Southwest's flights were canceled Monday, even more than on Sunday. Delta had to reduce its flights by 8% on Monday. 18% of Southwest's flights were late, according to FlightAware.

Southwest is focused on point-to-point service, unlike competitors who use hub-and-spoke systems to funnel passengers to large airports.

Buffalo, the hardest-hit urban area in the storm's path, is served by Southwest. Dallas, Phoenix and Las Vegas are some of the places where Southwest has major operations.

There were other tie-ups at Southwest and other places. A worker shortage, an air-traffic control interruption and bad weather caused a four-day disruption that wiped out 3,100 flights. The airline cut almost a third of its flights over a six-day period in 2007.

(Updates cancellations in first and seventh paragraphs.)