Mediterranean climate zones, as classified, are found on west coasts around the world at particular latitudes. The typical weather pattern is, roughly, six rainy months and six dry months, with mild, wet winters and warm, or hot, dry summers.
Despite what some people may bemoan, we do have seasons, but their patterns are dictated by our climate type. We'll not have your fall hardwood colors, or snow-bound winters, and you'll not have our figs, olives or grapes.
San Francisco has a modified Mediterranean climate, due to its location and setting. Our summer-cold coastal surface waters create our signature fog, and our hot interior valleys to the east, where hot air rises, pull cooler air inland to replace the rising air and contribute our summer winds.
Here's an informational graphic that can better illustrate the cycles:
What this means on a practical level is: bring outerwear. Your weekend may be fog-bound and windy. Some days the fog barely recedes. If you go out on a boat in the bay, it can be even windier and colder.
If a high-pressure system parks itself off shore, we will have pleasantly warm sunny days that may even become hot.
While San Francisco may be fog bound, weather in nearby locations may be significantly warmer and clearer, as in the east or south bay.
As attendees, fantastic tote bags are in your future, so you will have a stylish place to stash your layers when the sun comes out.