Doppler Weather Radars marked the beginning of a new era in detecting and forecasting weather. In addition to detecting areas of precipitation called echoes, the Doppler Radar also detects movement and intensity of the precipitation. The radar also detects wind velocity and direction by detecting the motion of objects either toward or away from the radar. These data are critical for identification of severe storms like tornados.

The jet stream is a fast moving rather narrow ribbon of air moving west to east that circles the globe in an almost continuous fashion. Jet streams are important because they are responsible for producing most of the winter storms in California. The polar jet is located well north of California but when it does move south it brings cold and wintry weather. The subtropical jet is usually located just south of California. Sometimes this jet can move north into California bringing warm moist air that can cause flooding through heavy rain and snowmelt. The jets are strongest during the cooler half of the year.