Understanding Our Local Microclimate

Mount Tam wears a wispy shawl of fog  |  post by Richard Pavek  |  photo by Melanie Rovens

Every day for the first ten days after I moved to the Yellow Ferry Harbor in mid-May 1978 I woke to sunshine and hot days. I felt like I was in summertime heaven! But that lasted for only two weeks when I woke to find a blanket of fog that covered the sun until noon. “Summer” was over! For nearly three months nothing but chilly morning fog that lasted until noon. Bummer!

Then I discovered that early morning sunshine was two miles up the road just over the Tiburon Ridge! Morning fog on the south side of Tiburon Ridge but not the north side?

Well that’s not all that that’s weird (excuse me, unique) about North Richardson Bay.

How about the hot, gusty afternoon winds that bedevil Marin City and the Gate 6 Road communities when two miles to the south downtown Sausalito is much cooler and calm?

Why are afternoon temperatures around North Richardson Bay typically 12-15 degrees cooler than San Rafael which is several miles to the north?

Why are the local tide charts so unreliable? Sometimes they are spot on but other times they underpredict highs as much as nine or ten inches.

These incongruities exist because the Headlands, the Tennessee Valley, the Mount Tam watershed, Tiburon Ridge, Ring Mountain, and the Tiburon-Belvedere Hills combine into a horse-shoe shaped band of hills that controls our North Richardson Bay Microclimate.

We live in a pocket formed by a ring of warm hills surrounding a cool bay. Early morning fog-laden southwesterly winds in spring and summer sweep over the ridges and uplands covering the western part of the ring in a fog blanket that slowly dissipates as it flows down Sausalito’s sun warmed hills—leaving Tiburon and Belvedere sunny and warm. By noon the fog usually abates, and all around the ring the air is warming in time for lunch.

Later in the afternoon, the Southwesterlies have shifted to become Westerlies, which, heated by the sun, come roaring across the headlands through the Tennessee Valley, to swirl and bluster, bedeviling the Northern end of Sausalito and Marin City. But when the winds don’t blow, Marin City’s flats and Sausalito’s docks may heat up to 100 degrees!

Across the Golden Gate in San Francisco fog covers most of the city for a good part of the day. Why? Because there are no eastern facing hills for the morning sun to warm!

Finally, the sun sets and the winds, having lost the sun’s heat, settle down. And so, we, the lucky residents of North Richardson Bay, retire to our TVs or our favorite book of the moment and relax. Just another day in Paradise…until the Big Rains come!