San Francisco is having one of its top-20-warmest years on record, but the city couldn’t keep a late fall chill away over the weekend. The City by the Bay broke a record on Sunday when its high only reached 50 degrees.
“Tule fog” was the main contributor to the record cold day on Nov. 30. It’s a type of fog that typically forms during the night and early morning hours from late fall through the beginning of winter. It is a type of radiation fog that occurs when longwave energy from the Earth escapes, cooling the air near the surface enough for low clouds and fog to form.
“It’s called a Tule fog, but that’s just a local reference to the phenomena that sets up in general, usually in the early winter,” explained Roger Gass, the lead forecaster for the Bay Area National Weather Service Office, to SFGATE…