New California Rainfall Normals Show a Downward Trend


Every decade, the 30-year normals that are the de facto climatological standard, are recalculated. Sometime within the next six months, an update from the 1981-2010 normals to the 1991-2020 normals will be published by NOAA and other agencies around the world. [See]
Until that date, below are close approximations of what those values will look like for a number of key stations around California, along with their historical normals through each station’s period of record.  It is interesting to note that over the past decade, all the California stations, except Eureka, shows a drop in their 30-year normals, averaging approximately 5%.
This shift was largely the result of the drought years across much of the state from 2011 to 2015 that pushed values downward. For example, the San Francisco average rainfall for the last decade (2011-2020) was 20.22”, replacing the average for 1981-1990 which had been 22.39”. The intervening decades of 1991-2000 and 2001-2010 had averages of 25.25” and 23.16” respectively.

Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services