Flash Flood Guidance

National Weather Service CNRFC Guidance
In Contra Costa County, storm runoff  comes fast and the water raises quickly in creeks. Residents and businesses lack time to prepare once a large storm is upon us.

The National Weather Service California Nevada River Forecast Center (CNRFC) produces several on-line products to inform the public on weather related issues. Flash Flood Guidance Maps are one of these products.

The Flash Flood Guidance Maps provide a map view of Contra Costa County colored similar to other maps they produce such as the Quantitative Precipitation Forecast (QPF) map. The Flash Flood Guidance can be generally summarized as follows:

Flash Flooding can occur when we experience...

  • Approximately 1 inch in one hour
  • Approximately 2 inches in three hours
  • Approximately 3 inches in six hours

Review the Flash Flood Guidance maps and become familiar with other weather links. Prepare early if you live in a flood prone area. 

Flood Preparedness

What to do if forecasts predict flooding  
If the 24-hour forecast is for two (2) inches of rain or more, and the other antecedent conditions are met, flooding may occur sometime in the next 24 hours.

If you live in a flood prone area, you should have a personal evacuation plan and keep an eye on the weather and the antecedent conditions. Monitor weather agency broadcast warnings via television and radio. Your personal evacuation plan should be implemented if you sense flooding may occur.