Monitoring Freezing Levels Across California: A Comparison Between Recent El Niño and Drought Winters

NOAA's Hydrometeorology Testbed (hmt.noaa.gov) was sponsored by the California Department of Water Resources (CA-DWR) to design, build, deploy, operate, and maintain a network of ten FM-CW precipitation profiling radars (a.k.a. snow-level radars) mostly near major watersheds across California. In this paper we use freezing-level measurements from these radars to investigate possible inter-annual variability in this important variable. Higher freezing levels increase the mountainous areas that are exposed to rain thereby increasing runoff that could lead to dangerous flooding. Lower freezing levels allow snowpack to accumulate over a wider range of elevations thereby decreasing runoff and allowing beneficial water storage for future use. The strong El Niño present during the winter of 2015-16 may be used as a proxy for climate change, i.e., when warmer sea surface temperatures are likely to exist globally. Although few winter storms occurred in each of the preceding three drought years, enough cases will be compiled to allow comparison between the latest strong El Niño winter and the three preceding winters that were weakly forced by ENSO.