Federal scientists say that La Niña — the phenomenon where Pacific Ocean waters off South America are cooler than normal — is underway this winter.

A commonly held assumption among many Californians is that La Niña means a dry winter is coming, and in years when the opposite occurs, El Niño, a wet winter is considered more likely.

So brown lawns and water rationing are just around the corner, right?

Not necessarily. Looking at historical records, there isn’t a clear pattern. In the Bay Area, La Niña years have been drier than normal only about half the time.