WRN - Flood Watch Vs Flood Warning

What is the difference between a Flood Watch and a Flood Warning issued by the National Weather Service?

  • Flash Flood Warning: Take Action! A Flash Flood Warning is issued when a flash flood is imminent or occurring. If you are in a flood prone area move immediately to high ground. A flash flood is a sudden violent flood that can take from minutes to hours to develop. It is even possible to experience a flash flood in areas not immediately receiving rain.
  • Flood Warning: Take Action! A Flood Warning is issued when the hazardous weather event is imminent or already happening. A Flood Warning is issued when flooding is imminent or occurring.
  • Flood Watch: Be Prepared: A Flood Watch is issued when conditions are favorable for a specific hazardous weather event to occur. A Flood Watch is issued when conditions are favorable for flooding. It does not mean flooding will occur, but it is possible.
  • Flood Advisory: Be Aware: An Flood Advisory is issued when a specific weather event that is forecast to occur may become a nuisance. A Flood Advisory is issued when flooding is not expected to be bad enough to issue a warning. However, it may cause significant inconvenience, and if caution is not exercised, it could lead to situations that may threaten life and/or property.

Flood or Flash Flood Watches

Much like our Severe Thunderstorm and Tornado Watches and Warnings, we issue Flash Flood Watches and Warnings.  Flood Watches are issued to inform the public, cooperating agencies, and other interests that the current and/or developing weather pattern is such that there is a potential for rapid flooding (also known as flash flooding), more widespread areal flooding, or river flooding.  The occurrence of flooding is neither certain nor imminent.  Persons in the watch area are advised to check flood action plans, keep informed, and be ready to take necessary actions if a warning is issued or flooding is observed.  A Flash Flood Watch may also be issued for a potential dam break.

Flood or Flash Flood Warnings

A Flood or Flash Flood Warning is issued to inform the public that flooding is imminent or in progress.  It focuses on specific counties, communities, streams, or areas. Flash Flood Warnings are issued for flooding usually occurring within 6 hours of heavy rain.  An Areal Flood Warning is issued for flooding that occurs more gradually, normally from prolonged and persistent moderate to heavy rainfall.  A River Flood Warning is issued when a river is forecast to go above its designated flood stage at the forecast point.

Areal Flooding vs Flash Flooding

These two types of flooding may be confusing, so we thought we would take a minute to try and clarify the difference between them.

A Flash Flood Warning is issued for flooding that normally occurs within six hours of heavy or intense rainfall.  This results in small creeks and streams quickly rising out of their  banks.   Dangerous flooding in areas near these creeks and streams, as well as low-lying flood prone areas, develops very quickly and is a significant threat to life and/or property.

An Areal Flood Warning is normally issued for flooding that develops more gradually, usually from prolonged and persistent moderate to heavy rainfall.  This results in a gradual ponding or buildup of water in low-lying, flood prone areas, as well as small creeks and streams. The flooding normally occurs more than six hours after the rainfall begins, and may cover a large area.  However, even though this type of flooding develops more slowly than flash flooding, it can still be a threat to life and property.

Flood Advisories

A Flood Advisory is issued when flooding that is not considered a significant threat to life or property is expected or occurring.   This usually deals with nuisance flooding problems, such as flooding in low-lying areas and areas of poor drainage, as well as minor flooding of streets and roadways.  This type of flooding causes some inconvenience, but is not generally considered a significant threat to life or property.  

Flood Advisories are normally issued as an Urban and Small Stream Flood Advisory. 

Other Important Information

Unlike our Severe Thunderstorms or Tornado Warnings, flood products are normally issued for extended periods of time.  These warnings are normally issued for 2 to 4 hours, or longer.  Even though rainfall may have subsided, flooding may persist for some time.  The longer warning time allows for rainwaters to recede while keeping the public aware that flooding is still occurring and there is still a threat to life and/or property in the warned area.  

Flood and Flash Flood Warnings will be transmitted on NOAA Weather Radio, and WILL alert your radio.  Advisories DO NOT alert your radio.