LATEST UPDATE (Friday): Holiday travelers faced the prospect of flight delays in the Northeast and mid-Atlantic on Friday, the busiest air-travel day of the Christmas period. It remained to be seen if delays would spike throughout the day like they had on Friday. (Full story: Christmas travel: Flight delays grow, some airlines waive change fees)

PREVIOUS UPDATE (Last updated Thursday at 10:10 p.m. ET): Delays slowed travelers at a number of airports Thursday as the busy Christmas air-travel period kicked into high gear.

Nationwide, only 231 flights had been canceled as of 10:10 p.m. ET, according to flight-tracking service FlightAware. But the tally of delays had spiked by Thursday evening from a mix of storms, wind and poor visibility that affected airports on both coasts.

But more than 7,020 flights were late at U.S. airports, creating headaches for air travelers Thursday -- one of the three busiest days of the Christmas/New Year's travel period. Friday (Dec. 21) is expected to be the busiest between now and Jan., according to both the Transportation Security Administration and the Airlines for America trade group.

Thursday's problems could spill into Friday as a developing storm moved out of the South and into the mid-Atlantic and Northeast. No mass cancellations were expected, but Friday could become another day marked by delays at certain airports.

On Thursday, the biggest problems were in Florida and at a handful of delay-prone airports in the Northeast and California, though more delays were cropping up late Thursday. A visibility-related ground stop had gone into effect in Atlanta, the world's busiest airport, around 7:45 p.m. ET.

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In the West, few flights were canceled at San Francisco, but more than 20 percent of Thursday's flights were behind schedule because of fog and cloudy weather. In Seattle, which grappled with strong winds, about a quarter of the day's flights were late, according to FlightAware's count.

But the bulk of the air delays came along the East Coast, where a developing storm sprawled from Florida north into New York and southern New England by early Thursday evening.

Near New York City, about a quarter of the day's flights had been delayed at Newark's Liberty airport in New Jersey. Delays were higher than normal at New York JFK and Philadelphia, but were more a nuisance than extreme disruption. In Charlotte, North Carolina -- a major hub for American -- few flights were canceled, but about 20 percent were late, according to FlightAware.

Airports across Florida grappled with sporadic delays much of Thursday as a long line of storms moved across the state. Orlando bore the brunt of the problem, with more than 1 out of every 3 flights behind schedule. Fortunately for travelers there, there were few cancellations.

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JetBlue waived change fees for Thursday travelers flying through three airports: Orlando, Sarasota and Tampa. JetBlue customers in those cities were allowed to make one no-cost change to their itineraries as long as they completed their rebooked flights by Saturday (Dec. 22).

Beyond JetBlue's Florida waiver, however, no other airlines had issued rebooking waivers because of the weather.

For Friday, potential problems remained for the mid-Atlantic and Northeast, where a mix of heavy rain and strong winds were forecast again at the delay-prone hubs serving New York City and Philadelphia. Boston also could see problems as sporadic storms and wind move into New England. The winds could linger into the Northeast through Saturday.

Disruptions are not expected to be extreme, but flyers traveling through the region should keep an eye on the status of their flights.

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