California Precipitation Map

Average annual precipitation from 1960 to 1990, as found from NOAA. This map permits zooming and panning to get a closer look of the wide variations in rain and snowfall depths across the state.

Maps such as this depicting precipitation depth as contours are known as isohyetal maps, which indicate areas with roughly equal precipitation. Data was retrieved from NOAA's National Climatic Data Center. More recent data is available, but the isohyets are not as smooth in data sets from the last decade. I thought it would be interesting to compare the precipitation contours over time, though it seems the more recent computer-generated contours are very blocky and look more like geometric polygons than smooth contours.

Pretty amazing that isolated areas in the Klamath Mountains receive as much as 150 inches of rain per year, while the heavily irrigated Imperial Valley receives 5 inches or less. Areas of the Transverse Range, north of the LA Basin actually receive significant precipitation depths, though engineers have a hard time harnessing this fickle supply that often comes in flashy torrential rain events and patchy snow storms.

Map projected in California Albers projection and design adapted from Mile Bostock's Iceland Topography map, which is a slight variation on Ziggy Jonsson's original.