More than 2,500 flights canceled as winter storms slam large part of nation

More than 2,500 commercial flights were cancelled and nearly 9,000 others were delayed as of Thursday morning, with snow, sleet and hail forecasted for a large swath of the country.

About 800 of the scrubbed flights were within, into or out of the United States Thursday, according to the flight tracking website FlightAware.com.

The Minneapolis-Saint Paul International Airport was feeling the brunt of what is expected to be a historic snowstorm with 10 inches of snow having already fallen since Wednesday. At least 30% of flights out of the airport were canceled Thursday morning and 20% destined for the airport were scrapped, according to FlightAware.

In the Northeast, an icy mix continued Thursday morning from New York state to southern New England, with heavy snow in northern New England and Maine.

Portland, Oregon, recorded 10.8 inches of snow on Wednesday, marking the second-biggest day of snowfall in recorded history in that area. More than 20% of flights out the Portland International Airport were canceled Thursday morning, according to FlightAware.

The National Weather Service has issued a blizzard alert for the mountains of Los Angeles County for the first time since 1989, the agency said. The warning is scheduled to take effect at 4 a.m. Friday and will last until 4 p.m. Saturday as the weather service forecasted 2 to 5 feet of snow and 75 mph winds at mountain elevations as low as 4,000 feet, and said flakes could fall around the Hollywood sign historical landmark.

But as of Thursday morning, the weather was not having a big effect on flights in and out of the Los Angeles International Airport, where 1% of flights were canceled.

With flight cancellations expected to grow as the weather gets worse, airlines are typically willing to rebook passengers on the next available flight. Since flights are scarce and some airlines are overwhelmed, customers may prefer a refund.

Any potential refund depends on a passenger's communication with the airline, Clint Henderson, a managing editor for news at The Points Guy, told ABC News in an interview in December.

"Be your own best advocate," Henderson said. "You really have to appeal to the airline directly -- there's no third party that takes care of it for you."

If an airline cancels a flight and a customer decides that he or she does not want to rebook an alternative one, the customer is entitled to a full refund by law, according to the Department of Transportation. That requirement applies no matter the reason for the flight cancellation, the agency said.

In such a circumstance, the customer can demand reimbursement directly from the airline, Henderson said.

"A lot of times airlines will try to give you a voucher but you're entitled to cash back," he said.