Comparison of AQPI X-Band and NEXRAD S-Band Radar-Estimated Rain Rates during an Extreme Atmospheric River Event

The Advanced Quantitative Precipitation Information (AQPI) project has installed several new X-band radars across the Greater San Francisco Bay Area. These strategically located radars operate at a very high spatial and temporal resolution, and complement the existing NEXRAD network by providing more detailed rainfall information across the region (Cifelli et al. 2024). An extreme atmospheric river event impacted the northern Bay Area during 24-25 Oct 2021 and produced record precipitation across the region, as well as very intense precipitation rates associated with a narrow cold-frontal rain band. This study compares radar-estimated rain rates from the local AQPI X-band radar and nearby NEXRAD S-Band radars to a variety of rain gauge observations across the area. The results show that the AQPI X-band radars did provide an improved estimation of precipitation in this case, confirming earlier work by Biswas et al. (2022), and also highlight how this improvement is modulated by precipitation intensity and other factors such as elevation and terrain orientation. Future work involves an extension of this case study to a more comprehensive analysis spanning a statistically significant sample of events. More information is available at: https://cw3e.ucsd.edu/aqpi/.