San Fernando Valley climate

The San Fernando Valley has been mentioned only in passing in previous studies of Southern California climate. The availability of temperature and rainfall measurements made on and near the city of San Fernando from 1878 to 1974, however, permits a closer look at Valley climate. The temperature record is missing for 25 years: 1904 to 1928; between 1878-1903 and 1929-1974 the Valley became progressively warmer, more so in winter than summer, especially in the urbanization phase after 1950. Rainfall data have been published for all years except three: 1904 to 1906. This record can be extended back to about 1770 from the reconstruction, by H. B. Lynch in 1931, of seasonal rainfall from numerous chronicles starting with the mission days around 1770 and ending in 1930. Combination of the reconstructed data with actual measurements taken at San Fernando has provided nearly 200 years of seasonal rainfall records. This series gives little evidence of any cyclical character in the rainfall picture. Weather station observing networks slowly evolved in the San Fernando Valley until the 1930s. Published information from these stations is included with a brief historical description of these stations to supplement San Fernando data and contributes toward a better understanding of Valley climate.