There are three main types of flood warnings issued by the NWS:
Flash flooding – a flood that occurs within 6 hours of excessive rainfall and that poses a threat to life and/or property. Ice jams and dam failures can also cause flash floods.
River flooding – any high water flow, overflow, or inundation event which is threatening lives and property along main stem rivers.
Areal flooding – any high water flow, overflow, or inundation in a defined area such as a group of counties or an area along a river or stream which threaten lives and property that is not covered by an river flood, or flash flooding. The main difference between flash floods and areal floods is that areal flooding applies to longer duration precipitation, (greater than six hours), causing slow rises on rivers and streams.