PRECIPITATION – Annual precipitation totals in excess of 50 inches per year are characteristic of the west slope of the Sierra Nevada north of Stockton, the west slope of the Coast Range from Monterey County northward, and parts of the Cascades.  Exception to this are totals that decrease to about 20 inches in the Monterey Bay area and parts of the San Francisco Bay area.  In the lee of the Coast Range yearly drop off to 15 inches in parts of the Sacramento Valley and to less than eight inches over most of the San Joaquin Valley.  The northeast interior portion of the State receives from 15 to 18 inches of moisture in a year.

The maximum intensity of precipitation for periods of 12 hours or longer which might be expected at intervals of 10 to 100 years is greater in portions of the San Gabriel and San Bernardino Mountains in southern California than anywhere else in the continental United States.

THUNDERSTORMS – Thunderstorms may occur in California at any time of the year.  Near the coast and over the Central Valley there appears to be no definite season.  The storms are usually light and infrequent.  Over the interior mountain areas storms are more intense, and they may become unusually severe on occasion at intermediate and high elevations of the Sierra Nevada.  In these mountain areas, thunderstorms, observed by radar at one point of another, average 50 to 60 days per year.  They usually occur when cool, moist air moves in to break a prolonged hot spell.