Bay Area Fog*
Tracker

Herb Caen on Bay Area fog

You may be drenched by a downpour that the natives assure you is merely "a wet fog." It hardly ever rains in San Francisco. But it wet-fogs quite a bit.

— Herb Caen's Guide to San Francisco, 1958

On SFChronicle.com, we don’t just track disasters – though (hint, hint) you can see the latest fires, earthquakes, and more). Now, thanks to the wonders of modern technology, you can follow San Francisco’s most famous weather phenomenon in near-real time. Say helllllo to Fog Tracker.

Let's get technical

In an effort to remove some of the (cough, cough) fogginess around how we got this data, here’s a brief summation.

The data for the Fog Tracker images comes from the National Oceanic and Atmospheric Administration’s GOES-17 satellite and includes visible clouds and fog formations, as well as visibility conditions in San Francisco.

Stop us if you’ve heard this one: GOES satellite data managed by the NOAA is available for free for use through Amazon Web Services. The images above come from GOES-17’s Band 2, also known as the red visible band. (Oooooh.) Band 2 has the highest resolution of the 16 bands (score!) and can help identify fog boundaries and cloud coverage. The red band cannot create a “true color” image on its own (aww, shucks), so these images use a blue-to-white color scheme to distinguish the darker land and ocean from the lighter clouds and fog. (Hooray!)

San Francisco weather condition data comes from Accuweather and is updated every 20 minutes. You’re on your own during the 19-minute intervals.

Special thanks to Brian Blaylock for his assistance with understanding GOES data. He’s one smart dude.