SAN FRANCISCO (KRON) – What would the City By The Bay be without its smothering companion filling the space between Victorians on a summer’s day?

But while it may be the city’s oldest resident, San Francisco’s fog only got its name relatively recently, when the Twitter account @KarlTheFog started in August 2010.

A 2012 image from NASA Earth Observatory shows Karl the Fog being pulled in through the Golden Gate to the Bay Area. (Photo courtesy National Aeronautics and Space Administration)

The account, which can boast almost 360,000 followers, was inspired by a faux British Petroleum account that sprouted up in the aftermath of the Deepwater Horizon oil spill in the Gulf of Mexico.

The account came back Jan. 20 from a two-year hiatus; its last tweet before that was about the San Francisco 49ers wining the National Football Conference championship.

“Moved in with my parents in Point Reyes at the start of the pandemic,” the Jan. 20 tweet states. “The free rent was great, but nothing beats hanging 6ft away from you.”

But the identity of the account holder remains as shrouded as the weather phenomena they represent.

During Karl’s hiatus, an account named Karla The Fog, @fog_karla, popped up to “pick up the void” left by Karl.

Karla told KRON4 in 2020, “Karl The Fog was around for a really long time. He disappeared and then there were the rumors that he left. Seeing a void and being a proactive, feminist Fog myself, I thought, ‘Well, why not?’”

The real Karl is formed when the heated air from the city rises, creating a low-pressure zone that sucks in cold, foggy air from above the Pacific. This is most common in the summer, which caused Mark Twain to (allegedly) say “The coldest winter I ever spent was a summer in San Francisco.” This is also why the fog is most prevalent on the westside, close to the ocean.