National Weather Service United States Department of Commerce

Flash Flood Guidance:

Flash Flood Guidance (FFG) provides a general indication of the amount of rainfall evenly distributed over various durations (in hours), necessary to cause small streams to overflow their natural banks. During heavy rainfall, accurate interpretation of the guidance consists of the combination of rainfall that has already occurred plus any additional rainfall that can be confidently expected to fall over the same location in the immediate future.

It should be noted that FFG values represent estimates of average soil moisture and stream flow conditions. Flooding may occur with less rainfall than indicated in areas of high rainfall intensities, impervious surfaces, or steep slopes.

1 hour values 3 hour values 6 hour values

Headwater Flood Guidance:

Headwater Flood Guidance depicts the approximate rainfall evenly distributed over various durations to cause selected streams to reach official NWS flood stage (may not necessarily coincide with the natural bank) at U. S. Geological Survey gauging stations. As with Flash Flood Guidance, these values are intended as general guidance.