Rain is expected to arrive in the Bay Area as early as this evening and continue through much of Thursday, National Weather Service officials said Tuesday.
The storm system will bring light rain and scattered showers with isolated thunderstorms to Central California, up to a quarter inch of rain in most areas and up to half an inch in coastal mountain areas, according to Bob Benjamin, a weather service forecaster.
It should clear in the Bay Area by Thursday night but heavier showers could persist in southern Monterey County through early Friday morning.
"We can expect a fairly decent wetting rain for most areas," Benjamin said.
Benjamin said that while it was too early yet to be certain, this May appears likely to be wetter than normal.
In an unfortunate coincidence, the rain is expected to arrive during Bike to Work Day, an annual event intended to encourage people to commute by bike.
The San Francisco Bicycle Coalition has organized "Energizer Stations" where riders can pick up snacks and gift bags during commute hours as well as commuter convoys and other events.
Coalition spokeswoman Ellie McCutcheon said all planned events would still go forward, despite the storm.
"We will have our energizer stations out there rain or shine," McCutcheon said. "We are really excited."
The coalition advises riders planning to commute in the rain to wear breathable layers with waterproof items on top, maintain visibility with bright colors and reflective materials - and ride a little more slowly and carefully than normal.
For more information on Bike to Work Day, go to www.sfbike.org. Tips on riding in the rain can be found at https://www.sfbike.org/news/9-simple-tips-for-biking-in-the-rain.