Weather delays at San Francisco International Airport and Oakland International Airport follow a seasonal pattern that most travelers never hear about. SFO is one of the most delay-prone major airports in the United States, and the main cause is not storms. It is the low summer cloud deck of the marine layer, which often hangs over the airport into late morning. On those mornings SFO lands fewer planes an hour, and the FAA holds San Francisco flights at their departure airports. The patterns are predictable by season and time of day, even though no one can say in advance which flights will be hit.
SFO, Fog, and Reduced Arrival Capacity
SFO's main arrival runways, 28L and 28R, run side by side only 750 feet apart. For decades, controllers used that layout to land planes in pairs in clear weather. Pilots could see each other and fly side-by-side visual approaches, which let SFO land up to about 54 planes an hour. When low clouds hid the approach, those paired landings weren't allowed, and the arrival rate fell to about 30 to 36, as little as half the clear-weather rate.
That changed in March 2026, when the FAA stopped allowing side-by-side approaches at SFO even in clear weather, after a review of the airport's parallel-runway operations. Controllers now stagger arrivals so that one plane stays ahead of the other. With Runway 1R back in service after repaving, SFO says it can handle about 45 arrivals an hour in fair weather and about 36 in low visibility.
So low clouds still slow SFO, but the drop is now closer to a fifth than a half. When arrivals fall behind, the FAA starts a ground delay program, holding SFO-bound flights at their departure airports. A morning fog at SFO can delay flights from New York or Chicago by an hour or more, even under clear skies there.
The worst delays come on mornings when the marine layer is thick and slow to break up. July and August are usually the most delay-prone months. On a typical bad day, a ground delay program starts early in the morning and runs until the clouds lift in late morning. The airport clears by early afternoon and operates normally through the evening. Flights due to arrive between 7 and 11 AM are the most vulnerable, and afternoon arrivals are much less likely to see weather delays.
Oakland as the Alternative
Oakland International Airport, on the East Bay shoreline about 11 miles from SFO, usually has fewer weather delays on summer mornings. It often sits away from the thickest marine air that pours through the San Bruno Gap toward SFO. It also has less traffic and does not depend on closely spaced parallel runways, so low clouds do not cut its capacity the same way. When SFO is running a ground delay program, OAK is often operating normally or with minor delays.
The trade-off is that OAK has fewer destinations, fewer terminal amenities and less frequent service to many cities than SFO. If you can be flexible about routing, it is worth checking both airports for the same trip during the summer months. On a day when SFO is restricting arrivals, an OAK flight can save an hour or more of waiting.
Which Months Have the Most Fog Delays at SFO?
The delay pattern at SFO is predictable by season, even if individual days vary. June through August carry the highest risk of morning fog delays. September and October usually bring improvement as the marine layer weakens and the Indian summer pattern takes hold. From November through April, winter storms can cause delays from wind and low clouds, but those events usually clear faster than the persistent summer pattern.
Spring, from late March through May, is often one of the better periods for on-time arrivals at SFO. The summer cloud deck has not fully set in, the storm season is winding down and clear days are common. Late fall and early winter can also bring stretches of high pressure with very clear skies. If weather delays are your main concern and your dates are flexible, July mornings are the time to avoid.
What Travelers Can Do
The most practical way to avoid summer weather delays at SFO is to book afternoon flights rather than morning ones. That does not guarantee an on-time flight, but it greatly reduces your exposure to the morning cloud cycle. Morning departures from SFO are less affected than arrivals, because their delays come indirectly from gate holds and late incoming aircraft.
Before leaving for the airport, check the FAA's national airspace status page for any ground delay program at SFO. When one is active, its expected delays are posted in real time. If you are connecting through SFO on a summer morning, an extra hour of connection time is a sensible buffer.
