Note: This post was originally published on May 20, 2014

“The coldest winter I ever spent was a summer in San Francisco.”

Mark Twain may never have actually said it himself, but that doesn’t make the statement any less true. 

As any naive tourist shivering miserably in a tank top and Bermuda shorts might attest to, San Francisco in the summertime can be one chilly town. Even on days when temperatures in nearby cities climb into the 90s, it’s not uncommon to find much of San Francisco shrouded in a thick blanket of fog, the mercury barely reaching 60 degrees Fahrenheit.

If you’re still a bit foggy (sorry, couldn’t help myself) about why that is, scroll through the great interactive explainer (above) created by Newsbound.

And for more inspiration, take a look at this beautiful timelapse film by Simon Christen. Below that, a short video by KQED’s Quest team digs deeper into the science of coastal fog.

  • Karl the Fog

    Great post about my cardiovascular system. I focus so much on my emotions, it’s good to hear how I actually work.

    • Cecilia Hinojosa-Einhorn

      The cutest post!

  • Hunter Cutting

    Great that you posted these beautiful videos!

    But please get the science right. Fog is not “pulled in” by heat in the Central Valley. It is pushed in by high pressure off the coast, pushed into the low pressure zone created by air rising due to heat in the Central Valley. A nuance, to be sure, but an importance difference, and getting it wrong clouds thinking about the basic physics of the way weather works (pun intended). Please get it right.


Matthew Green

Matthew Green runs KQED’s News Education Project, a new online resource for educators and the general public to help explain the news. The project lives at

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