What is the weather like in San Francisco/Sunnyvale during May? Is there any need to bring winter clothes?

To the best of my memory, it’s snowed in the San Francisco Bay Area about once every 10 or 11 years. People took a lot of pictures but the snow didn’t stick for more than a couple of hours. It was all melted by the afternoon. There are a few nearby mountain peaks that may get snow every four or five years but that’s not where the cities are. Midwestern or eastern winter clothes are things to leave at home.California, unlike a lot of the US, has microclimates. A microclimate is a relatively small area. Because of hills, mountains, prevailing winds and/or proximity to the ocean, two areas that are fairly close together may have different weather. San Francisco and Sunnyvale are in two different microclimates, even though they’re not that far apart. If you look at a local weather forecast for the area, the afternoon temperatures are usually 10–15 degrees different on the same day.San Francisco sits right on the coast of the Pacific. Its weather is affected by the cool fog that comes from the ocean, which keeps it about 60 degrees during that time of year. The problem is that the fog gets you wet, and then the wind comes along and makes you cold. Just like you may shiver when you get out of a pool and step into the wind, you will probably get very cold on a foggy and windy night in San Francisco. It’s the combination of wet and wind that can be cruel.Sunnyvale is to the south and is inland. There’s a range of small mountains and hills between it and the ocean. It’s typically much warmer and sunnier in Sunnyvale than in San Francisco at the same time on the same day. It generally has much less wind and it almost never is foggy. It may get a very light frost every once in awhile during the winter when the cold winter air sits in the broad valley that it’s in, but it’s not a big deal. An easterner would probably laugh at what we call “frost.”If you’re going back and forth between the two cities, dress in layers. You’ll need a light jacket or parka to keep you warm and dry in San Francisco, but it should be easy to take off when you get to Sunnyvale. Wearing a sweatshirt or sweater under the parka may help make you comfortable if you go out at night in San Francisco. Again, layers are the key.