Miss Jo's San Francisco

IT’S THE START OF SUMMER FOG SEASON in San Francisco and the questions have already started.

“What’s it like without summer ?” friends and familia ask Miss Jo. “Don’t you get tired of the cold ?”

Even after living in the City since 2005, it’s still not easy to come up with simple answers to explain what’s up with San Francisco’s famous fog, which most days from mid-June-August creeps out of the Pacific Ocean in late afternoon and gradually marches across town by sunset.

At the same time, Miss Jo has to explain that San Francisco summers aren’t lost causes. Before the fog arrives, there are usually several hours of sun. There are many days like today when summer is left intact with no sign of fog and you better not leave the house without SPF 15 on. Some neighborhoods are also foggier than others.

Thanks to the fog and general breezy coastal Pacific Ocean weather, it’s a rare summer day when San Francisco swelters, which is just fine by Miss Jo, who grew up in the prickly Texas heat and sweated for years in Washington, D.C.’s 100-degree humidity in pantyhose.

When the fog starts moving inland, temperatures fall to around 50 degrees from daytime highs that vary from 60-85 degrees, depending on the neighborhood micro-climate. Generally, the farther south of downtown you go like the Mission District, there’s less fog, more sun and higher temps.

Either delicately thin or ominously dense, fog in any form puts the kibosh on thoughts of warm-evening barbecues. Last summer, a German house guest was so befuddled by the cold that she refused to accept how fog routinely pulled the shade on perfect summer days— and her long-imagined California vacation.

“When is it going to get warmer ?” she asked daily, while laughing off Miss Jo’s explanation and advise to take a sweater with her to the beach— or seek warmer climes just across the Bay for a dose of exceedingly hot weather.

Miss Jo will also never forget her first fog season in 2005 when her sister’s family was visiting. The fog was so thick it felt like Alfred Hitchcock’s dry-ice machine was stuck on high. The best photo taken the entire week was of her sister and oldest niece bundled up on the couch.

The fog turned out to be a perfect backdrop for getting used to a new city in a rented house in the shape of a mini castle, with turret, found on Craigslist.

For San Franciscans, the fog is a passing inconvenience, easily balanced by sunny summer mornings and afternoons that emerge when nature’s wet blanket— the only moisture during six months without rain— evaporates.

So why is there fog ? It’s really nature’s way of air conditioning points inland where daytime temperatures can top 100 degrees.

The phenomenon, seen elsewhere along the northern California coast, starts when cold coastal air mixes with warm summer air, which creates chilly vapor. The vapor gets sucked eastward by afternoon winds stirred up by hot inland temperatures that rise and expand, according to San Francisco’s Exploratorium kids’ science museum.

When there’s a balance between inland and coastal temperatures, fog takes the day off.

Photo by Miss Jo: Fog settling over Cole Valley.


Here’s some heavy San Francisco fog on the march: