UNDATED -- Thick fog in parts of the Bay Area Monday morning forced San Jose International Airport to halt all of its flights for more than an hour and delayed about half of San Francisco International Airport's flights, airport officials said.

About 20 flights were affected when the San Jose airport halted its arrivals and departures between about 8 a.m. and 9:15 a.m., airport spokesman Rich Dressler said.

Several approaching planes that were scheduled to land at the San Jose airport during that time were diverted to Oakland International Airport and an airport in Reno, Dressler said.

Oakland airport spokeswoman Rosemary Barnes said the Federal Aviation Administration alerted the airport, requesting that it be prepared to accept at least five diverted flights from other Bay Area airports until 10:30 a.m.

"We're prepared to make sure there is adequate gate and ramp areas for the diverted flights," Barnes said. She said no major delays occurred at the Oakland airport this morning.

Dressler said weather-related delays are relatively common nationwide during the holiday weekend.

"A lot of flights were affected across the country this Thanksgiving weekend," Dressler said. "We're fortunate we're not snowed in or have any other severe weather issues."

Departures have resumed and, as of about 9:30 a.m., were slowly returning to their normal schedules. Arriving flights were not expected to begin landing until 10:30 a.m., according to Dressler.

All flights should have resumed by noon, Dressler said.

Fog typically closes the San Jose airport once or twice a year, but this is the airport's "first major fog situation of the season," Dressler said.

At SFO, half the inbound and outbound flights remained delayed due to fog around 9 a.m., duty manager Lily Wang said.

Most late flights are delayed by about an hour, and there is no estimated time when the flights will return to schedule, Wang said.

"We just don't know when it's going to clear," Wang said of the fog.

Weather in other parts of the country is delaying flights as well. Flights to Chicago, where it is snowing, are delayed by about an hour.

Travelers and those picking up passengers from the airports are advised to check with their carriers before heading to the airport, Dressler said.