What differentiates a normal rainfall year from a dry year?
Most of California’s precipitation comes from storms moving across the Pacific Ocean. The path followed by the storms is determined by the position of an atmospheric high-pressure belt that normally shifts southward during the winter months. On average, 75 percent of California’s annual precipitation occurs between November and March, with 50 percent occurring between December and February. A persistent Pacific high-pressure zone over California during December through February predisposes the water year to be dry.
