Evaluating rainfall measurements over Sonoma County
April 1, 2014
Sonoma County is situated in a flood-prone region of California, and because of the mountainous terrain and remoteness from operational radars, it is generally believed to lack adequate radar coverage. A new study evaluating rainfall measurements of National Weather Service operational radars over California’s Sonoma County was published in the February 2014 issue of the Journal of Hydrometeorology. In this study CIRES and NOAA Earth System Research Laboratory scientists analyzed 58 significant precipitation events in Sonoma County observed over the six-year period by the San Francisco KMUX and Davis KDAX operational radars. The results show that precipitation estimates strongly depend on the type of observed rainfall.
The figure at right shows different types of rain observed by a profiler at HMT’s Cazadero (CZD) field site in Sonoma County, and the corresponding hourly rainfall accumulation estimates for these rain types obtained from KMUX radar measurements. Six different precipitation types were considered in this study: 1) rainfall producing radar bright band (BB) – a radar signature caused by the transition of frozen to liquid precipitation as it falls through the atmosphere, 2) no bright band (NBB) shallow rainfall, which was not detected by the radar, 3) NBB rainfall detected by the radar, 4) NBB convective rainfall, 5) virga (precipitation that doesn’t reach the ground) detected by the radar, and 6) erroneously detected rainfall. The results of this study will improve operational radar precipitation data in Sonoma County.
A special correction for radar measurements was suggested as part of this study. This correction will improve the quality of radar-based precipitation measurements in Sonoma County.
Contact: Sergey Matrosov
Matrosov, Sergey Y., F. Martin Ralph, Paul J. Neiman, Allen B. White, 2014: Quantitative Assessment of Operational Weather Radar Rainfall Estimates over California’s Northern Sonoma County Using HMT-West Data. J. Hydrometeor., 15, 393-410, doi:10.1175/JHM-D-13-045.1.
