San Francisco summers don’t have too much in common with summers in other places. You will see billowing white fog, the majestic product of sea spray, wind and Central Valley heat, San Francisco summers are characteristically overcast and cool, while the marine layer usually burns off by the afternoon. Another unusual feature of our weather are our micro-climates. San Francisco is a city with microclimates and submicroclimates. Due to the city’s varied topography and influence from the prevailing summer marine layer, weather conditions can vary by as much as 9°F (5°C) from block to block, sunny in one neighborhood and overcast in another.
Our region is known as the San Francisco Bay Area and can have a wide range of extremes in temperature. In the basins and valleys adjoining the coast, climate is subject to wide variations within short distances as a result of the influence of topography on the circulation of marine air. The San Francisco Bay Area offers many varieties of climate within a few miles. In the Bay Area, for example, the average maximum temperature in July is about 64 °F (18 °C) at Half Moon Bay on the coast, 87 °F (31 °C) at Walnut Creek only 25 miles (40 km) inland, and 95 °F (35 °C) at Tracy just 50 miles (80 km) inland.
So, if you are a little cold today, you can get on BART after class and go to Walnut Creek for some much warmer weather in only 35 minutes!