NEW YORK >> It’s official: This winter was the worst for fliers in the 20 years that the government has been collecting data.

During the first three months of this year, U.S. airlines canceled 4.6 percent of their flights, the Department of Transportation announced Tuesday.

Mother Nature is mostly to blame, with a relentless wave of snow and ice storms paralyzing airline traffic across the nation.

But airlines are also quicker to cancel flights these days, sometimes a day in advance of a storm. The shift in strategy came in response to new government regulations, improvements to overall operations and because canceling quickly reduces expenses.

In May 2010, a new DOT rule took effect prohibiting airlines from keeping passengers on the tarmac for three hours or more. So, airlines now choose to cancel blocks of flights to avoid potential fines of up to $27,500 per passenger or $4.1 million for a typical plane holding 150 fliers.

Making things worse for travelers, airlines have been cutting unprofitable flights and packing more passengers into planes. When flights get canceled there isn’t anywhere to put the stranded passengers; some end up waiting days to secure a seat on another flight.

In March, JetBlue had the highest cancellation rate among the bigger airlines: 2 percent of flights. That was closely followed by the merged American Airlines and US Airways, canceling 1.9 percent. Southwest Airlines and United Airlines both canceled 1.1 percent and Delta Air Lines 0.2 percent.

Some of the highest flight cancellation numbers came from smaller regional airlines that are operated by other companies on behalf of the major airlines. ExpressJet, which flies regional planes for American, Delta and United, scrapped 5.1 percent of its March flights. American Eagle canceled 4.1 percent of its flights and SkyWest — another subcontractor — nixed 2.3 percent of its scheduled flights.