There are many types of flooding statements that can be issued by the National Weather Service. Maybe you received an “Areal Flood Advisory” due to prolonged rain from a coastal storm, or a “Flash Flood Warning” notification on your phone because a thunderstorm was dumping torrential rain? Either way, it's important to know the differences between flood watches, advisories, and warnings, as well as what to do if one is issued.
A Flash Flood Watch means that weather conditions are favorable for rapid flooding to occur within the specific watch area. It does not mean that flash flooding is certain or is already occurring. Rather, it is possible that flooding can occur on a shorter time frame (for the duration of / just after the event). When this type of statement is issued, it is important for those within the watch area to keep informed and be prepared for necessary action if a Flash Flood Warning is issued.
A Flash Flood Warning is issued when rapid or “flash” flooding that normally occurs during or just after heavy or intense rain is already in progress or imminent. This is an urgent message and action should be taken immediately, as dangerous flood waters can rise rapidly and catch people off guard, posing a significant threat to life and property. When this type of statement is issued, people who live in flood prone areas should move to higher ground immediately. NEVER drive through flooded roadways - Turn Around, Don’t Drown!!
Graphic courtesy of NOAA.
An Areal Flood Watch means that weather conditions favoring a prolonged period of moderate to heavy rainfall that can cause more gradual flooding over a larger area is expected. Specific places that may flood in this larger area include poor drainage / urban zones, small streams and creeks, and low-lying / flood prone locations. Just as in a flash flood watch, it does not mean that areal flooding is guaranteed, but rather is possible, and individuals should be prepared to take further action if necessary.
An Areal Flood Advisory is issued when this gradual flooding of low-lying places, small streams and creeks, and urban / poor drainage areas is already occurring, but is not a significant threat to life or property. Rather, it will just cause inconveniences (i.e. road closures from flood waters), but caution should still be exercised so that the situation does not become life-threatening.
An Areal Flood Warning is more urgent and serious than the advisory. Gradual but ongoing flooding (normally about 6 hours after the rainfall begins) in some of the locations mentioned poses a significant risk to life and property. Although different from flash flooding, it is still strongly urged for those within the warned area to move to higher ground and to never drive through flooded roadways.
