Low visibility caused flight delays Monday at Philadelphia International Airport. Soupy skies - a combination of low clouds and fog - led to delays averaging 30 minutes for arriving flights, airport officials said.

According to the Federal Aviation Administration website, weather also caused delays for holiday travelers at Newark Liberty International Airport, and, for a while, at Reagan National Airport in Washington.

Across the country, the FAA said, arrivals and departures were delayed 15 minutes or less on average.

"We remain on an arrival delay averaging 28 minutes," Philadelphia airport spokeswoman Victoria Lupica said shortly after 4 p.m.

"There are some delays in arriving and departing flights, but the airlines are not reporting any cancellations due to weather."

Amtrak experienced some delays in the New York City area Monday afternoon due to switching problems in the tunnels in and out of the city, said spokesman Craig Schulz. "We were in pretty good shape the rest of the day, and we're looking pretty good right now," he said at 5 p.m.

NJ Transit buses and trains were running on time, said spokesman William Smith. The only delays, which are ongoing, he said, were caused by Amtrak track work at New York's Penn Station.

Philadelphia airport officials advised travelers to allow extra time to catch flights and to check with their airline, or call 1-800-PHL-GATE or visit the airport's website, www.phl.org, to click on flight information.

"The rain doesn't affect it. It's really the clouds," Lupica said. The airport had a handful of delayed departures, and one canceled morning flight - a 6:46 arrival from Ithaca, N.Y., she said.

US Airways spokesman Todd Lehmacher said earlier Monday that flights out of Philadelphia were "slow going," but that as the weather improved on-time performance was 75 percent systemwide, with only a handful of canceled flights nationally.

"The big issue was Washington Reagan National, where an unexpected fog bank moved across the airport," Lehmacher said. A ground stop in Washington resulted in 17 diversions of aircraft to other airports. The ground stop was later canceled and "landings have resumed," he said.

US Airways, with 437 daily flights out of Philadelphia, operated on a holiday schedule, with 14.5 percent more flights across its network. "All due to anticipated high demand. Booked load factors are high," Lehmacher said.

Lupica encouraged anyone picking up a passenger at Philadelphia to park in the garages or short-term lots, or use the free cellphone waiting lot for periods of up to 30 minutes.

Travelers were reminded not to wrap gifts because they may have to be opened for inspection during security screening. This applies to both checked and carry-on items, the airport said.

Low visibility Sunday caused delays of about 90 minutes. The airport did not have any stranded passengers overnight Sunday, Lupica said.

"That's a testament to the airport and the airlines working together, and making sure the travelers are getting to their end destinations," she said.