Explainers

Flood Advisory, Watch, Warning and Flash Flood Warning explained

By Ryan Hall, Y'all Weather Desk · Published

Written by our automated news desk from National Weather Service data.

A Flood Advisory means be aware, a Flood Watch means be prepared, and a Flood Warning or Flash Flood Warning means take action. A flash flood is the fast kind, starting within about six hours of its cause, and driving into flood water is how most flood drownings happen.

Flood Advisory, Watch, Warning and Flash Flood Warning explained

Key points

  • Flood Advisory: be aware. Flooding should not get bad enough for a warning, but it can still cause real trouble.
  • Flood Watch: be prepared. Conditions are favorable for flooding, but it is not a sure thing.
  • Flood Warning: take action. Flooding is happening or about to happen, usually along larger streams and rivers.
  • Flash Flood Warning: take action. A sudden, violent flood is happening, about to happen, or highly likely.
  • Never drive into flood water. More than half of flood drownings involve a vehicle.

A Flood Advisory means be aware, a Flood Watch means be prepared, and both a Flood Warning and a Flash Flood Warning mean take action now. A Flash Flood Warning calls for immediate action in a flood-prone area because a sudden, violent flood is imminent or occurring. These alert meanings come from National Weather Service definitions.

Flood Advisory

A Flood Advisory means be aware. The Weather Service issues it when flooding is not expected to be bad enough for a warning. That does not make it harmless. It may cause significant inconvenience, and if people are not careful, it can lead to situations that threaten life or property. Use caution and pay attention.

Flood Watch

A watch says the ingredients are lined up. Conditions are favorable for flooding. It does not mean flooding will happen, only that it is possible. This is your time to get ready, before anything is rising.

A Flash Flood Watch works the same way for the fast kind of flooding. Current or developing conditions are favorable in and close to the watch area, but flash flooding is neither certain nor imminent.

Flood Warning

A warning means stop getting ready and start acting. A Flood Warning says flooding is imminent or already occurring. It is the one issued for flooding along larger streams and rivers, where there is a serious threat to life or property. It usually comes with forecast river levels.

River flooding is usually the slow kind. A river flood warning typically comes 6 hours or more after the cause, and it is usually tied to widespread heavy rain, snowmelt or ice jams.

Flash Flood Warning

A Flash Flood Warning means take action. It means flash flooding is in progress, imminent, or highly likely. If you are in a flood-prone area, move immediately to high ground.

What makes a flood a flash flood

Speed. A flash flood is a rapid and extreme flow of high water into a normally dry area, or a rapid rise of a stream or creek above a set flood level. It begins within six hours of the cause. That cause can be intense rain, a dam failure or an ice jam. The exact time cutoff can vary in different parts of the country.

A flash flood can take anywhere from minutes to hours to develop. It can even happen in a spot that is not getting rain at that moment. Ongoing flooding can also turn into flash flooding when intense rain sends a sudden surge of rising water through.

Why you never drive into flood water

Flooding kills more people each year than any other thunderstorm-related hazard. The CDC reports that over half of all flood-related drownings happen when someone drives a vehicle into hazardous flood water. The next largest share is people walking into or near it.

The National Weather Service gives these benchmarks:

  • 6 inches of fast-moving water can knock over an adult.
  • 12 inches of rushing water can carry away most cars.
  • 2 feet of rushing water can carry away SUVs and trucks.

You also cannot tell what is under the surface. The road may have collapsed beneath the water. That is why you never drive around barriers blocking a flooded road.

What to do

  • Advisory: be aware and use caution.
  • Watch: be prepared for possible flooding.
  • Flood Warning or Flash Flood Warning: take action. In a flood-prone area under a Flash Flood Warning, move to high ground immediately.
  • At any flooded road, turn around. It is never safe to drive or walk into flood water. Turn Around Don't Drown.

When one of these is up for your area, check our live warnings.

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Sources

https://ryanhallyall.com/news/flash-flood-warning-vs-flood-warning-and-flood-watch