Forget about spring -- today will feel more like a day straight out of February.
A cold Gulf of Alaska system will spill rain over the Bay Area around midday with rain amounts in the .33 to .50" range in the North Bay and lesser amounts further south. Highs will mainly be in the 50s to possibly a few low 60s, and probably feel cooler than that, thanks to some breezy conditions.
While totals aren't expected to be too heavy, it will be another round of cool and wet weather. Remember what it felt like on Mother's Day? Monday will be a little heavier, especially north of San Francisco. The Sierra could get snow 6"-12" above 7,000 feet. That's pretty outstanding for mid-May -- unless you have to drive through it.
Due to the cold nature of this system, ice pellet/hail showers are possible at times. There's a slight risk of thunder too, but mainly in the Solano County-Sacramento/San Joaquin Valley areas.
Things should dry out fairly quickly late this evening and into tonight as brisk northwest winds kick in and help to dry things out. Showers should be done by Tuesday morning with warming and drying conditions from midweek into next weekend.