San Francisco's Summertime Stratus Deck
I spent the end of May in the San Francisco Bay Area and a few days in the city itself. As the heat of summer was taking hold in the D.C. area, as well as the rest of the country, a massive stratus deck parked over the cold waters of the eastern Pacific Ocean had other plans for parts of coastal California. In seeking photo opportunities during the "June Gloom," one can use an understanding of weather and geography much more than just hoping for good luck.
Keep reading to learn more about the stratus deck and to see some photographs of San Francisco.
Summer in San Francisco is typically one of the cloudiest times of the year. While inland locations warm to daily highs between 80 and 100, cold sea surface temperatures average in the mid-and upper-50s along the coastline. These differing temperature regimes help to create pressure gradients that can cause an onshore flow of clouds and cooler marine air.
Daytime heating causes rising air and lower pressure just above the land surface, while cooler offshore air tends to sink and cause higher pressure just above the ocean surface. The resulting pressure gradient creates a surface wind blowing from the ocean toward the land (from high pressure to low pressure).
Higher up in the atmosphere, the warmer and rising inland air is drawn horizontally out to sea to replace the cooler, sinking air. Clouds are created as the warmer air moves over the cooler air. These clouds get pushed inland by the onshore flow when it is present. During summer, onshore winds last well into the night before relaxing prior to dawn when the interior is coolest.
Unlike spring and fall -- the warmest times in San Francisco -- finding a truly clear day between May and July can be a difficult task. But unless the clouds are unusually thick, there is often at least some blue sky to be found from day to day. You just need to know where to look. My last visit was in spring of 2004, and while watching weather conditions, I tried to focus on different spots this time.
The trick is to focus on sections of the city that are on the eastern (and especially southeastern) sections of the peninsula. Fortunately, this includes much of the downtown with its many iconic buildings as well as large portions of the residential districts that contain parks and hills overlooking the city.
I stayed in the Mission District while visiting a friend which placed me east of the 900-foot-plus Twin Peaks. This ridge of small hills served to displace the onshore flow -- and thickest clouds -- to my north and south, leaving my location under a gap with daytime sun two of the three days. (As I was leaving, the cloud deck was thickening thanks to an approaching storm and the final day was the cloudiest.) After a day trying to dodge the clouds, I decided to climb the mountain to get a closer look.
After ascending 900-plus feet on steep roads and dirt paths, I found myself at the "summit" of Twin Peaks. Weather conditions were quickly changing, and the cloud deck was just feet above my head (and at times at my level). Winds were gusty from the west -- somewhere around 20mph sustained. It was a worthwhile trip up, but rather cold and misty at the top. I stayed long enough to snap a few mostly-documentary photos and headed back down.
On a clearer day, Twin Peaks provides stellar panoramas of the city.
San Francisco is know for its hills, so I had to hit at least two of them. Bernal Heights -- peak about 500 feet above sea level, or a bit more than half as tall as Twin Peaks -- was an obvious destination since it was close to where I stayed. I arrived at the heights right before sunset, when the onshore flow was very strong following daytime heating in the interior valleys. Low clouds screamed by from west to east, and the lighting was ever-changing.
In the picture above, a bit of the clear "gap" in the clouds mentioned earlier can be seen (see that image larger). In a picture on Wikipedia from the sky the gap is clearly evident, with a protruding Sutro Tower sitting atop Twin Peaks.
My last day featured a visit to Angel Island that put me out into the San Francisco Bay to view the fog from yet another angle. Cruising by the Golden Gate Bridge (see large photo), I watched the clouds filtering in as if yearning to journey through the bay. By afternoon the clouds gradually burnt off enough that there was a dividing line of air masses right overhead at Angel Island.
On the return trip to San Francisco, I observed the warm continental air temporarily winning its ever-continuing battle with that of the chilly Pacific. In the afternoon sun Mount "Tam" popped out of the clouds on the horizon. The gray surely returned later that day.
San Francisco during this time of year may require some patience from a photography standpoint, but there are also numerous rewards. In a city that is in such a geographically fascinating spot, it is not hard to get some spectacular views in, even when coastal low clouds and fog are in the forecast.
See many more photos at my San Francisco photo page on Flickr.
| June 11, 2009; 10:45 AM ET
Categories: Education, Photography
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