“The coldest winter I ever spent was a summer in San Francisco.” Quotes like this are often brought up in conversations about the weather in the San Francisco Bay Area. With its relatively unchanging climate, even stereotypically warm seasons in the Bay Area stay on the cooler side.
And yes, sometimes it gets a bit chilly. But the most remarkable thing about Bay Area weather is the time of year it gets cold or hot, not how warm or cold it is. Unlike most places in the Northern Hemisphere, the hottest months of the year are in September and October, right as Berkeley High School students begin school.
Sophia Novick-Prucher, a sophomore at BHS, is deeply familiar with the way heat disrupts learning. “My English classroom is the hottest classroom in the entire school and I have it sixth period,” she said. This is backed by data — Novick-Prucher checked the temperature monitors in different classrooms one sweltering September day and found that none were hotter than C204, her 6th period classroom located on the south side of the C building. This class was so hot, in fact, that one day Novick-Prucher’s class didn’t get any work done “because it was too hot to focus on anything,” she said.
Hot fall weather can also interfere with sports or other activities. Rye Tewksbury, a junior at BHS, finds that skateboarding in hot weather is “very inconvenient,” as he often skates in fairly baggy, heavy clothes.
Ren Senánt-Giraud, a BHS junior who grew up in Toulouse, France, finds the weather here in Berkeley baffling. “You usually start fall,” Senánt-Giraud said. “Then in September, mid September, a huge wave of heat waves. Why does that happen? That’s so weird. We don’t have that, at least not in southern France or anywhere in France.” Why, then, are the summers here cooler than the fall?
According to Warren Blier, a meteorologist at the NOAA (National Oceanic and Atmospheric Administration) for the San Francisco Bay Area, the autumn heat is caused by reduction of the cool sea breeze winds. The direction of the ocean currents off of the coast bring cold water from the north, which causes a marine layer, or a mass of cool and wet air, to form.
During the summer months, the sun heats up air further inland, heating it up and reducing the air pressure. Air moves from high pressure to low pressure, so the cooler, higher pressure marine layer on the coast blows inland. As a result, “in Berkeley on a typical day in June or July, the west winds start picking up,” said Blier. Because the marine layer off the coast is so cool and wet, these winds are responsible for the sometimes cloudy San Francisco skies during the summer.
In the fall, as the inland regions receive fewer hours of daylight, the lack of heating in the interior means that the sea breezes that kept the Bay Area cool in the summertime become weaker. Weaker winds means less cold air, and students in Berkeley start to complain about the heat that sometimes occurs in early autumn.
The Bay Area climate is known as a Mediterranean climate, which “tends to be characterized by a kind of mild cool, on and off wet winter and then a dry summer season with moderate temperatures unless you get too far away from the coast,” said Blier. “It’s actually considered to be among the most pleasant climates that exist on Earth, from the perspective of many people, to live in.”
Perhaps we should appreciate our mild weather a bit more. According to Senát-Giraud, eating lunch outside in Toulouse will not end well. “You will get burnt. You will become a puddle of human flesh.”