Investigating periodicity in the long term precipitation record of Donner Summit, California

Donner Summit, California has the longest precipitation record from any high-elevation snow-dominated environment in the western United States. Water year 2000 will complete its 13Oth year of record. Ancedotal evidence suggests periodic trends in the long term snowfall record of Donner Summit. However, the measurement of snowfall is frequency dependent, making it a less-than-ideal gauge by which to compare one season to another. Correlation coefficients are derived between annual Donner Summit precipitation values X(t) and X(t+k), where k is delta t. These coefficients are combined with a periodic term to derive a spectral density which describes the amount of variance per interval of frequency within the historic record. Peak frequencies from the spectral analysis are applied to the historic data to test for periodicity. The relative strength (or weakness) of periodic cycles may improve perspective on long term trends in mountain weather, vital information for water managers.