California Precipitation Data (Federated)

CDEC precipitation data consists of direct observations from a statewide sensor network — over 140 agencies currently contribute data through more than 1,100 remote stations and roughly 8,500 sensors, transmitted via the state microwave system, GOES satellite, and automated data exchange. Data is publicly accessible at no cost; however, users should be aware that data are provisional and subject to revision. This entry is organized into four groups of resources: composite precipitation indices, regional station groups, discovery and programmatic access tools, and reference and documentation resources.

• **Composite Precipitation Indices** — Three primary indices maintained by DWR: the Northern Sierra 8-Station Index (8SI), San Joaquin 5-Station Index (5SI), and Tulare Basin 6-Station Index (6SI). Each is computed as an unweighted arithmetic mean of cumulative water-year-to-date precipitation across its member stations, and is used by DWR in developing water supply forecasts each water year as part of Bulletin 120. Both daily and monthly index values are provided, along with the underlying component-station data for each index (8 stations for 8SI, 5 for 5SI, 6 for 6SI) for users who need station-level detail rather than the composite value alone.
• **PG&E and Oroville/Feather River Regional Groups** — Six regional precipitation station groups: five operated by Pacific Gas & Electric (PP1–PP5) and one operated by DWR covering the Oroville/Feather River area (OR1). These groups report a mix of daily and hourly data depending on station, and several groups share member stations with one another (for example, PP3's six stations are entirely a subset of PP1's eleven, and PP2's four stations are entirely a subset of PP4's roster) — see individual resource descriptions for full station lists and overlap details.
• **Discovery and Programmatic Access** — Tools for discovering stations not itemized in this entry and for retrieving their data directly. These include a searchable station directory that can be filtered by sensor type, station lists organized geographically by river basin, a general-purpose query builder for retrieving daily or monthly data from individual CDEC stations, and the DWR-maintained Python package cdec_maps for programmatic and automated access to station metadata and time series.
• **Reference and Documentation** — Supporting resources for interpreting and contextualizing CDEC precipitation data, including a statewide water-year monthly precipitation reference reports, format, organized by reporting period or water year, quality-controlled human-readable precipitation summaries, and documentation of CDEC data flags used to indicate data quality, status, or other conditions associated with reported observations. **Scope.** This catalog entry provides metadata and links for a selected set of CDEC precipitation resources and is not intended to reproduce the full CDEC precipitation catalog or provide comprehensive statewide precipitation coverage. CDEC’s broader network includes hundreds of additional stations and products across multiple operators and watersheds that are not individually represented here. For the authoritative data, current products, additional stations, interactive plots, and other precipitation resources, users should access CDEC directly at its precipitation website. The source data and additional data and plots can be accessed directly from CDEC's website (cdec.water.ca.gov/snow_rain.html).