As many readers know, I have been tracking Grass Valley temperatures at the local national weather station since 2005. The average May Temperature in Grass Valley for the last 43 years has been 58.22 ºF. This last month the average temperature was 53.33 ºF, almost five degrees cooler than the long term average.
If we look a longer period from 1909 to 1966, when the Grass Valley station was not located at the wastewater plant, the average was 54.29 ºF It is interesting that the current month is much closer to the longer term 58 year record, than the shorter 43 year record.
The difference in the two long term records could be due siting issues, or the PDO shift that took place in 1977 and lasted to about 2003, or both. For many years the weather station was at the Empire Mine. Neither location was the best for taking accurate local temperatures, except maybe in the 1960s when it was in Ray Stein’s backyard in Grass Valley.
Later today, I will see if I can find a graph of Grass Valley temperatures.