The entire West enjoyed a mild start to the winter, with balmy temperatures throughout December to finish out 2024.  As shown in the figure below, California saw steady weather with temperatures in the mid-fifties, and with little variation from day to day and no days with significant cold.  And while the state of California saw a burst of precipitation in the lead-in to December, giving snow build-up in the Sierras a boost to start out the winter, most of December was underwhelming from snowpack standpoint, with current SWE lagging behind normal levels by approximately 25%.  The Pacific Northwest was plenty wet and is seeing healthy hydro output currently thanks to the rainfall (and relatively warm temperatures), but CAISO hydro output held steady from November to December.

Figure 1. California Daily Average Temperature and Difference from Normal (F)