For people who have been around the Bay Area it is nothing new that within 20km or so the temperatures can drop by 10 degrees or more. For those about to arrive – be aware.
The Bay Area has strong microclimates, which is especially apparent in the summer months when San Francisco can be in the clouds for days and the peninsula is pumping hot. Basically the Pacific Ocean, basins and valleys are responsible for great weather disparity. In the Bay Area, for example, the average maximum temperature in July is about 64 °F (18 °C) in Half Moon Bay on the coast, 87 °F (31 °C) at Walnut Creek only 25 miles (40 km) inland, and 79 °F (26 °C) in Palo Alto.
We had several occasions where we had planned a beach day in Half Moon Day and it turned out to be a ‘stay in the garden’ day. We would leave Menlo Park and half way through to HMB, just riding over the crest of the mountain range; we could see the fog rolling in. In the end we often decided that HMB could also be enjoyed in the fog. A good indicator whether HMB is going to be beautiful, is to check out the traffic on the weekend. When cars pile up already at the reservoirs it can well take you 2 hours to get to HMB.
Similar, when going to San Francisco we learnt that it is always a good idea to pack jackets and wear lots of layers. Temperatures can change walking from one block to the next.
We had visitors from overseas and we only had one day to show them Golden Gate bridge. From the San Francisco we were not able to even identify the red paint of the bridge. Luckily we decided to drive to Sausalito and half way through the bridge the fog cleared and we had the most amazing view from the Marine Headlands.
Always keep the microclimates in mind and remember, it is not always what it seems. Go ahead enjoy your planned trips and don’t let weather determine your day.