CHICAGO (Orbitz) -- Here's what to expect on Sunday at some of the busiest U.S. airports:

Newark Liberty, LaGuardia, John F. Kennedy, Washington Dulles and Philadelphia: Rain showers and en route thunderstorms will likely slow inbound flights by 60 to 75 minutes throughout the day.

Reagan National, Baltimore Washington and Charlotte Douglas: Thunderstorms and heavy rain may lead to arrival delays averaging 60 minutes throughout the day.

No delays are expected at other major U.S. airports. The Flying Forecast is updated frequently throughout the day as developments warrant.

Travel resources

• Airport security measures
• Airport parking, traffic, weather

How early do I need to check in for my flight?

If you're checking baggage, arrive at the airport:

• at least 90 minutes prior to a domestic flight
• at least two hours prior to an international flight

Following are some of the airlines that allow online check-in. Some also provide airport-specific check-in times.

• AirTran
• Alaska Airlines - Airport check-in times
• American Airlines - Airport check-in times
• Continental Airlines - Airport check-in times
• Delta Air Lines - Airport check-in times
• Midwest Airlines - Airport check-in times
• Northwest Airlines - Airport check-in times
• United Airlines - Airport check-in times
• US Airways - Airport check-in times