I have two use cases in mind:

(1) Delivery-bot. A car that drives itself to drop off a package and only delivers on non-rainy days. (if you need delivery on a rainy day, you pay extra for a person-driven delivery service. Otherwise the package waits at the warehouse)

(2) Transport option for people who can't or shouldn't drive themselves - too old, too blind, too young, or physically impaired. The self-driving car takes them where they need to go when weather permits, otherwise they have to call a cab or van service as a backup option.

(Much of California only has a couple weeks of rain per year.)