This photo posted this morning by Redditor blueski shows the fog rolling in/burning off from the vantage of 20th and Noe. This may or may not be attributable to the approach of summer, but if you need a primer on why SF gets summer fog, a.k.a. "intrusions by the marine layer," you can read that here.

The weather this week, by the way, is just supposed to get warmer through Friday.