When the weather turned warm earlier this week, any tried-and-true local could tell you that summer had arrived ahead of schedule.
San Francisco summers peak in mid-September, two months later than other parts of the country, said Jan Null, a meteorology consultant who was the lead forecaster with the National Weather Service’s Bay Area office for 35 years.
Or, as Noah Stolmaker, a 24-year-old web developer who lives in the Mission, put it, “As soon as you have to be stuck indoors, the weather gets nice.”
The unusual heat felt by residents this week had more to do with what wasn’t happening in the weather world than what was, Null said.
The fog and low temperatures characteristic of the city’s early summer months can be attributed to the atmosphere’s attempt to achieve equilibrium.
San Francisco Bay is typically bordered by a mass of cold, high-pressure air, a giant of Northern California weather patterns affectionately dubbed the Pacific High by weather wonks. As the summer sun heats the Central Valley, the cold air moves toward the warmer air, creating an onshore breeze along the coast that carries fog and cool ocean temperatures with it.
“It’s like having a fan over a tray of ice,” said Null.
That pattern changes in late fall. The jet stream, a fast-flowing river of air to the north of us, begins to creep southward, pushing the Pacific High south in turn. “Just like in your car, when you turn our natural air conditioning system off, things get cooking real fast,” Null explained.
And cook they did. San Francisco had a recorded high of 99 degrees Fahrenheit on Tuesday, shattering the previously held daily record of 89, set in 2003. It is advised to stay in an air conditioned-room to stay cool and avoid heat exhaustion.
Some didn’t seem to mind. “It’s no big deal. You just gotta sleep naked,” said 26-year-old Carina Lomeli, a local artist who is originally from Arizona.
Proud to be the aunty of this young lady