THE SUMMER WINDS HAVE RETURNED!

The geography of northern California is uniquely shaped to create some of the finest sailing conditions on the planet.

Photo by John Arndt

BY CAPTAIN RAY

 

The geography of northern California is uniquely shaped to create some of the finest sailing conditions on the planet. The arrangement of ocean and land, mountains and valleys, and high and low pressure systems is perfectly aligned in the San Francisco Bay Area. Perfect, that is, if you are a sailor! Let’s take a look at what we as sailors have going on for us.

 

First, of course, is the Bay itself: a large, open body of water, almost completely free of underwater hazards. (There are some submerged rocks that are potentially dangerous to big ships, but these rocks are deep enough to be of no concern to sailors.) The Golden Gate provides access from the Bay to the ocean for those that want it, yet is narrow enough (seven-tenths of a mile at its narrowest) to prevent ocean swells from entering. This keeps the surface of the Bay relatively smooth even when the ocean has 15- to 20-foot swells. Compare this with Monterey Bay just 100 miles to the south, which is completely open to the ocean and subject to its moods.

 

The next geographical feature to consider is the Central Valley. Both its location and size contribute to its importance in the creation of our sailor’s paradise. As we know, it gets hot in the valley in the summer. Air temperatures in the 80s and 90s are normal and over 100 degrees is not unexpected. This hot air rises, creating an area of low pressure throughout the Central Valley. Think of this low-pressure system as a weak, partial vacuum, drawing air into itself to replace the air that has risen.

 

The replacement air is not able to come from the east. In that direction, there is a 10,000-foot wall (the Sierra Nevada Mountains) blocking any inflow. However, to the west out over the ocean there is an area of high pressure, where air is descending onto the Earth’s surface and flowing outward in all directions, including toward the coast. This air will flow naturally from the area of high pressure to the area of low pressure. All that is needed is a pathway for that flow. The Golden Gate, the San Francisco Bay, the San Pablo Bay and the Carquinez Strait provide that pathway, all the way from the ocean to the Central Valley.

 

It’s the difference in temperature (and therefore pressure) between the hot Central Valley and the cool, often foggy coast that gets this air flowing. That difference can be as much as 50 degrees in as little as 50 miles. It can be 55 degrees at Ocean Beach while at exactly the same time it’s 105 degrees in Vacaville. I don’t know of any other location with this kind of temperature difference in such a short distance, without significant change in elevation.

 

The final piece of advantageous geography is the effect of the coast mountains. When air is squeezed through a narrow opening, it accelerates—this is called the Venturi Effect. This effect is exactly what happens at numerous places along the California coast. The San Bruno Gap (which caused the infamous winds in Candlestick Park) and where Highway 92 crosses the peninsula on the way to Half Moon Bay are two examples. The Golden Gate, however, is the only sea-level gap in the coast mountains. The distinction makes it a most efficient Venturi.

       

The air is pushed against the coastal hills by the oceanic high pressure at the same time it is sucked in by the low pressure in the Central Valley and accelerated as it is squeezed through the Golden Gate by the surrounding hills. It then flows across San Francisco Bay, where it is gratefully and enthusiastically used by sailors of all kinds. Board sailors, kiteboarders, mono- and multihull sailors all revel in this extraordinary sailor’s playground.

 

Ray Wichmann is a US SAILING-certified Ocean Passagemaking Instructor, a US SAILING Master Instructor Trainer, and a member of US SAILING’s National Faculty.  He holds a 100-Ton Master’s License, was a charter skipper in Hawai’i for 15 years, and has sailed on both coasts of the United States, in Mexico, the Caribbean and Greece. He is presently employed as the Master Instructor at OCSC Sailing in the Berkeley Marina.