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 late afternoons from mid-June-August creeps out of the Pacific Ocean 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, once the previous day’s fog lifts in the late morning. Many days like today, brilliantly sunny days are left intact.

Some neighborhoods are also foggier than others. Often the Mission is barely touched, but you can  count on the Sunset and Richmond getting blanketed.

Likewise, 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  humidity.

Either delicately thin or ominously dense, fog in any form puts the kibosh on thoughts of warm-evening SF barbecues.

Last summer, a German house guest couldn’t grasp how fog routinely pulled the shade on perfect days— and her long-imagined postcard California vacation.

“When is it going to get warmer ?” she asked daily, while laughing off Miss Jo’s advise to take a sweater with her to the beach— or go across the Bay or down the Peninsula for seasonally hot weather.

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 coastal northern California fog ?

The phenomenon starts when the ocean churns up cold air that mixes with warm summer air, creating a wet, chilly vapor over the water’s surface.

The vapor moves inland as it gets sucked along by hot inland  temperatures that are rising and creating a void for the cooler air.

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

Photo by Miss Jo: Fog settling over Cole Valley; Fog settling over the City in July, taken from Mt. Tam in Marin County; Miss Jo’s friends from St. Louis, Billy, Kup & Chris in July inside the Golden Gate; Fog covering St. Ignatius Church on Lone Mountain and Cheryl Ann @ Ocean Beach in June afternoon fog.