Flood events in Contra Costa County, California The flood events on record, by date and by year

The NWS collects event reports from a variety of sources, which include (but are not limited to): county, state, and federal emergency management officials, local law enforcement officials, SKYWARN spotters, NWS damage surveys, newspaper clipping services, the insurance industry, and the general public, among others.

The National Weather Service reports property and crop damage estimates using available data at the time of event reporting. These values should therefore be considered broad estimates. Damage amounts are not adjusted for inflation.

Zone (NWS Forecast Zone): A zone is a geographic area defined by the NWS for issuing forecasts, watches, and warnings. While zones often align with counties, they can also represent smaller or subdivided areas within a county to account for differences in weather conditions, such as elevation or proximity to water. Larger-scale events—such as heat, cold, drought, and winter storms—are typically recorded by zone.

The words of the agency. Source: NOAA NCEI, Storm Events Database, page "Frequently Asked Questions", copied on 2 Oct 2026.

Date of the data: NCEI storm events through 30 Jun 2026. Event types on this page: Flood, Flash Flood, Coastal Flood, Lakeshore Flood.