Air travel in the United States improved after a rocky weekend that left thousands of flyers stranded by thunderstorms in Florida, technology problems at the busiest domestic airline and labor problems at another carrier.

However, airlines that do much of their flying in Florida were still struggling Monday, especially Spirit Airlines.

And airlines were bracing for another round of storms that were forecast to hit the Dallas area, home to American and Southwest, Monday night.

Airlines scrubbed more than 650 U.S. flights by late Monday afternoon, according to tracking service FlightAware.com. That followed the cancellation of more than 3,500 flights, about one in every 13, over the weekend.

Thunderstorms led the Federal Aviation Administration to limit flights over much of Florida and briefly halt flights at several airports in the state on Saturday. That caused ripple effects across the country for the rest of the weekend, and some travelers reported having to wait before they could be put on another flight.

"It's spring-break season, so unfortunately there is no worse place to have bad weather than Florida right now," Henry Harteveldt, a travel-industry analyst for Atmosphere Research, said Monday. "The airlines are scrambling to get people where they want to go, they're working to get planes to and from Florida. It's going to take a couple days."

On Monday, Spirit, which is based in Miramar, Florida, canceled more than 250 flights, or just over 30% of its schedule. The airline said it was recovering from bad weather in Florida and elsewhere over the previous several days.

"It takes time to get our crews and planes back into place after multiple days of weather and restrictions," Spirit spokesman Erik Hofmeyer said. "We're seeing improved operating conditions, and we expect to move toward resuming our normal operations over the next few days."

JetBlue Airways, which flies frequently between Florida and the Northeast, canceled about 140 flights, or 13% of its total for the day.

Southwest Airlines, which operates more domestic flights than any airline, was doing much better on Monday — about 60 cancellations, 1% of its schedule, after scrubbing more than 900 flights, or about 13% of its total, Saturday and Sunday. The airline also suffered what it called intermittent technology problems over the weekend.

Southwest's unusual point-to-point route map means that many of its planes stop in Florida at some point during a normal day. By contrast, American, Delta and United run so-called hub-and-spoke networks in which flights radiate outward from a few key airports. That keeps planes in one part of the country insulated from bad weather in other places.

Alaska Airlines, the fifth-largest U.S. carrier, canceled about 40 flights or 5% of its schedule Monday. Over the weekend, the airline seemed to blame the pilots' union. Off-duty pilots have picketed at airports and an investor conference by the Seattle-based airline to protest the slow pace of contract negotiations over the past three years.

David Koenig and Julie Walker report for the Associated Press.

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