Airlines may be headed for more than $600 million in weather-related losses as winter storms have triggered the most flight cancellations since the government began tracking the data in 1987, Bloomberg reported.

Almost 20,000 flights were scrubbed last week alone as snow blanketed U.S. airports such as Chicago’s O’Hare International, a hub for United Continental Holdings Inc. and American Airlines, according to researchers FlightStats and FlightAware.com. Since Nov. 1, airlines have canceled nearly 90,000 flights.

That would push carriers’ net revenue loss to about $629 million, based on the average estimate of $7,000 for each scrapped flight, said Vaughn Cordle of AirlineForecasts LLC, which builds financial models for investors. His projection factors in lost fare revenue, which would be slightly offset by fuel and labor savings.

Cancellations could rise this week, with National Weather Service forecasts calling for a chance of snow tonight and Thursday in Atlanta, the biggest hub for Delta Air Lines Inc., and ice and snow late tomorrow and the next day in Dallas-Fort Worth, home to American’s largest operations.

Delta is alone so far in quantifying first-quarter weather fallout, saying Jan. 18 it would have a $30 million net reduction in revenue from scrapping 4,000 flights in its hometown of Atlanta last month. That’s about $7,500 a flight.

“I can’t believe I’m talking about snow again,” Delta CEO Richard Anderson told employees in a Feb. 3 message. “When we’re seeing record or near-record snow across the heartland and the Northeast, that definitely has an impact on our operation and airline operations all over the U.S.”

The previous worst season for cancellations occurred from November 2000 through February 2001, when airlines failed to operate 76,851 scheduled flights, or 3.93 percent, according to data from the U.S. Bureau of Transportation Statistics.