Fog has swallowed the Golden Gate Bridge. The fireworks might be spectacular anyway

Fog is in the forecast Saturday night as San Francisco prepares to launch its big fireworks display from the Golden Gate Bridge to celebrate the nation’s 250th birthday.

It will be the first time in the bridge’s 89-year history that fireworks have been fired from the span in July. Both prior bridge fireworks shows, in 1987 and 2012, were held in late May. But the July Fourth show comes with one very San Francisco problem.

Fog reached the Golden Gate Bridge by midafternoon Saturday, roughly 5½ hours before the 9:30 p.m. fireworks show. Webcams at Crissy Field showed the south tower fading in and out of low clouds while the north tower disappeared entirely. A camera on Sutro Tower, which sits at 833 feet, showed the top of the marine layer right at its level, putting the cloud deck near the height of the bridge towers.

This is not necessarily bad news. When fireworks explode above a fog deck, they light the clouds from above, turning the marine layer into a giant screen that glows with each burst. Shells that punch through the top of the fog leave trails of color below and starbursts above.

What you can see

Pat Dyas of Pyro Spectaculars, who is running Saturday’s show, said some of the most stunning photographs in the show’s history came from a year when the fog was thick enough to swallow the barges but thin enough for shells to break through the cloud tops.

That means the bridge will glow through the fog Saturday night, but the show won’t be invisible and may be visually stunning at times. The towers are loaded with pyrotechnics up to the top spars at 746 feet. The biggest shells burst at about 1,000 feet and spread up to 1,400 to 1,600 feet. With the marine layer top near 800 feet, those shells should punch through the fog and explode in the clear air above.

The two barges in the bay face a tougher situation. They launch from water level, so every shell has to climb through roughly 800 to 1,000 feet of fog. Only the largest will break through. Most of the barge show will be color pulsing through the clouds.

Crissy Field and Marina Green put you closest to the bridge but inside the fog. You will hear and feel every shell. The bridge will glow, but the biggest bursts may flash above you.

The show runs about 15 minutes. Bring layers. Temperatures at the waterfront will be in the mid-50s, with winds around 15 mph.

Historical context

In recent years, San Francisco’s July Fourth fireworks have been launched from barges in the bay near Fisherman’s Wharf and Pier 39, about 3 miles east of the Golden Gate Bridge. That location is farther inside the bay and generally more sheltered from the lowest cloud cover.

Moving the launch site to the Golden Gate Bridge puts the show directly in the path of the marine layer. Cool, moist air pushing in from the Pacific reaches the Golden Gate first, making low clouds and fog a much bigger concern than they would be farther east along the waterfront.

A Chronicle analysis of July 4 hourly weather observations from 2011 to 2025 shows how often low clouds have moved into the worst height range for fireworks visibility. Using reports from Oakland San Francisco Bay Airport and wind data from a state-run weather station on the bridge, the Chronicle compared cloud ceilings with the height of the bridge roadway and towers.

In roughly 1 in 4 years, the cloud base landed in that zone, where fireworks could be partially or completely obscured.

Clouds may interfere this year, but that does not mean the show is doomed. The safest forecast is to bring layers and expect the view to vary block by block and shoreline by shoreline.