“Flash Flood Warning!” “Flood Watch!” “Flood Warning!”
We hear these terms more often than not during monsoon season across the desert southwest and, with tropical like downpours that hurricane season brings across the U.S., do we really know the difference between these terms and what they ACTUALLY mean? Let’s break down the definition of each term.
What is the difference between a flash flood and a flood?
FLASH FLOOD: A flash flood is caused by heavy or excessive rainfall falling in a short period of time, generally less than 6 hours. They can occur within minutes or a few hours of excessive rainfall. They can also occur even if no rain has fallen, for instance after a levee or dam has failed, or after a sudden release of water by a debris or ice jam.
FLOOD: A Flood is an overflow of water onto normally dry land. The inundation of a normally dry area caused by rising water in an existing waterway, such as a river, stream, or drainage ditch. Ponding of water at or near the point where the rain fell. Flooding is a longer term event than flash flooding and may last days or weeks.
Now that you have an understanding of the difference of a flash flood and a flood, here is a breakdown of the possible flooding alerts you may find yourself in in the future:
FLASH FLOOD WATCH: Issued generally when there is the possibility of flash flooding or urban flooding over an area within the next 36 hours.
FLASH FLOOD WARNING: Issued when flash flooding is imminent, generally within the next 1 to 3 hours. Usually issued based on observed heavy rainfall (measured or radar estimated), but may also be issued for significant dam breaks that have occurred or are imminent.
FLOOD WATCH: Issued when there is the possibility of widespread general flooding over an area within the next 36 hours.
FLOOD WARNING: Issued when a river gauge has exceeded, or is forecast to exceed, a predetermined flood stage.
FLOOD ADVISORY: Issued when flooding is imminent or occurring, generally within the next 1 to 3 hours, but is not expected to substantially threaten life and property.