Pacific Climate Forcing of Multidecadal Springtime Minimum Temperature Variability in the Western United States

Trends toward an earlier spring season onset in the western United States have been increasingly documented and are of interest to many different users of climate information throughout the region. Studies, however, have not adequately quantified the variability of spring season temperatures on multidecadal time scales. This study examines the spatio-temporal variability of spring season minimum temperatures in the western United States as a function of multidecadal Pacific climate variability for the period from 1925 to 1994. Spatio-temporal variations in minimum temperature patterns, as determined by a principal-components-based regionalization analysis, indicate a significant statistical relationship between March and April minimum temperatures and multidecadal Pacific climate variability, measured diagnostically using an index of the Pacific Decadal Oscillation (PDO). Anomalous temperature patterns associated with cool phases of the PDO are evident in the Pacific Northwest region during March, whereas warm phases are evident in the Southern Coast region during April, suggesting a possible association with canonical interannual El Niño-Southern Oscillation (ENSO) impacts. These results, suggesting a strong and thus far uncharacterized relationship between spring temperature minima in the West and the PDO, have implications for an improved understanding of multidecadal climate dynamics, including the detection and attribution of recent temperature trends, as well as climate-driven environmental impacts such as growing season length and intensity.