The Advanced Quantitative Precipitation Information (AQPI) system is a regional project that uses enhanced weather radar to track atmospheric rivers. AQPI was funded in 2016 by a grant from the California Department of Water Resources (DWR) Integrated Regional Water Management Program (IRWM) awarded to Sonoma Water and participating Bay Area agencies. National Oceanic and Atmospheric Administration (NOAA) and the Cooperative Institute for Research in the Atmosphere (CIRA) built the AQPI system and delivering the AQPI end-product to these agencies.

The AQPI system provides X-Band and C-Band weather radar information that increases the accuracy of weather forecasting and response systems throughout the Bay Area. Improved forecasting assists flood agencies, emergency responders, wastewater plant managers, reservoir operators, and water managers in responding to extreme weather events in a timely fashion.

The University of California San Diego, Scripps Institution of Oceanography, Center for Western Weather and Water Extremes (CW3E) now operates the AQPI system with funding from federal, state, and local governments since the DWR grant ended in summer 2026.

The Problem

When big storms like atmospheric rivers hit California, current technology does not provide forecasters with the detailed information needed to inform reservoir operations, flood protection, combined sewer-stormwater systems and emergency preparedness. Accurate and timely precipitation information is critical for making decisions regarding public safety, infrastructure operations, and resource allocations.

Standard weather radars, originally designed to look up into Midwest thunderstorms, are often unable to give an accurate picture of what is happening just above the complex landscape of California’s coastal mountain ranges, where precipitation can be heaviest. Improved precipitation monitoring and prediction in the San Francisco Bay region enhances public safety through early warning and storm tracking when hazardous weather events come onshore.  This is the goal of the AQPI system. 

The DWR funded project installed four X-Band radars and one C-Band radar that cover most watersheds in the Bay Area (Figure A). Additional X-Band radars (not funded under this DWR grant such as the X-band in Santa Cruz) will provide data to the AQPI system. See Figure A below for map with radars and coverage of the SF Bay Area AQPI system.

Figure A. Map of SF Bay Area AQPI  X-Band and C-Band radar locations and coverage.

As of March 2026, one C-band radar and five X-band radars are operational. These radars are located in Marin, Sonoma, San Mateo, Santa Clara, Contra Costa, and Santa Cruz Counties. Radar locations include:

• Sonoma Water– Operating a temporary X-band radar since 2018, located near the Sonoma County Airport.  A permanent X-Band radar was deployed in March 2023 on the same site, the Sonoma Water Treatment Plant. 
• Valley Water  –   Since 2016 has operated a temporary X-Band radar at the Penitencia Water Treatment Plant. A permanent X-Band radar was deployed in July 2019 at the same location.
• San Francisco Public Utilities Commission (SFPUC) – Deployed an X-Band Radar on Sawyer Ridge in San Mateo County in August 2025.
• East Bay Agencies Partnership – In December 2022, a partnership of East Bay agencies deployed an X-Band radar on Rocky Ridge, adjacent to the Las Trampas Wilderness area. The Rocky Ridge radar became operational in 2023. This partnership includes East Bay Municipal Utility District, East Bay Dischargers Authority, Contra Costa County Flood Control & Water Conservation District, Alameda County Flood Control & Water Conservation District, Alameda County Water District, and Zone 7 Water Agency.
• Santa Cruz County Flood Control and Water Conservation District deployed an X-Band radar on a county building in August 2022, funded through a grant from DWR’s Statewide Flood Emergency Response Grant program. The radar will send data to the SF Bay Area AQPI system.
• C-Band Radar - Regional partners collaborated to deploy a C-Band radar on the peak of Barnabe Mountain in western Marin county. The C-Band radar covers the Pacific Coast and also areas inland to complement the X-Band radars, improving precipitation and stream flow forecasting throughout the region. 

Flooding is a major concern in the Bay Area. See below in Figure B, where AQPI radar provides a more accurate picture of rainfall in Santa Rosa, to better assess the potential for flooding. Note - Warmest colors represent highest rain volume.

Figure B.  NEXRAD vs. AQPI Radar Imagery

Figure C Spatial Resolution of AQPI X-band at Rocky Ridge (left) vs. NEXRAD S-band in Davis (right)