The Bay Area’s winter tradition of heavy fog and low clouds rolled through San Francisco International Airport’s runway areas Tuesday, limiting departures and arrivals to one of two runways and delaying flights from morning till mid afternoon.

Up to one-third of departures and arrivals at the airport were halted between 9 a.m. and 3 p.m. as pilots could not see farther than a half-mile, Duty Manager Michael Brown said. Officials said residual delays continued until 9 p.m. or 10 p.m. Tuesday.

Flights were delayed an average of an hour but some waits were longer, Brown said. Neither the airport nor the Federal Aviation Administration had same-day statistics Tuesday but Brown estimated that about one-third to one-fourth of the flights were halted.

Passengers with delayed flights may have actually turned out to be the lucky travelers Tuesday. When the fog was thickest in the morning, SFO arrivals had to land at airports as far away as Reno, Nev.

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The shortest flights and those on the smallest aircrafts were most affected, Brown said. Most flights traveling to or from farther east than St. Louis were unaffected but there were a few international delays that may have been caused by the haze. The planes hit worst by the delays were smaller aircraft with less advanced instrument landing equipment, he said. SFO officials did not know how many planes were affected by the foggy conditions.

By the time both runways opened at 3 p.m., visibility had increased to three miles, Brown said.

Shuffling traffic around happens quite often this time of year because of the area’s weather, FAA spokesman Ian Gregor said.

While the weather is typical for this time of year, the amount of delays was “relatively uncommon,” Brown said.

In case the delays continue until today, airport officials advised passengers to contact their carrier before leaving their homes.

mrosenberg@examiner.com