Flood Forecast Information

Flooding is more likely to happen when the soil is already wet and streams are running high from recent rains.

The current watershed wetness can be related to the amount of recent rainfall at rain gauges. Information from the rain gauges is presented on our Rain Map and Rain Gauge Page.The data at these links shows how much rain has fallen in recent time periods and is updated every 20 minutes.  The critical rainfall conditions to watch for are listed below. 

If the critical 7-5-3 rainfall conditions shown below are met or nearly met, and the National Weather Service forecast is for two (2) inches of rainfall in the next 24 hours flooding of the local streams is possible. Click the QPF map below to see the 24 hour forecast.
Critical Rainfall Conditions:
7" - Season’s Rainfall
5" - 30 Day Rainfall
3" - 7 Day Rainfall 

Critical Rainfall Forecast:
2” – 24 Hour Rainfall

Under these conditions, pay attention to radio, TV, or internet flood warning information. The National Weather Service forecasts and advisories should be monitored.

*QPF = Quantitative Precipitation Forecast
For more information on watershed wetness conditions, we created a detailed Excel tool created for monitoring NWS data and our rain gauges, go to our Flood Forecast Tool page.

See also our 7-5-3-2 handout on this topic.
See also April 6, 2011 presentation - (PDF - 9.7MB)

Questions about this Flood Forecast Information can be directed to the Sr. Hydrologist at (925) 313-2000.