About Gridded Flash Flood Guidance:
The 12 National Weather Service (NWS) River Forecast Centers (RFC) across the continental United States (CONUS) produce Flash Flood Guidance (FFG) products for the purposes of helping NWS Weather Forecast Offices (WFOs) monitor and forecast flash flooding events. Flash Flood Guidance is an estimate of the amount of rainfall required over a given area during a given duration to cause small streams to flood. These estimates are based on the current soil moisture and stream flow conditions for the area. The RFCs issue FFG grids at 4-km resolution for 1-, 3-, and 6-hour rainfall durations.
About Headwater Guidance:
Headwater guidance is the basin averaged rainfall required to produce flooding at an RFC basin outlet.