Flood watch vs flood warning
These are National Weather Service alert levels, and they are separate from the flood stage readings on this site. A gauge tells you what the water is doing at one point; an alert tells you what the Weather Service expects for an area.
The alert levels
- Flood Watch — Conditions are favourable for flooding. Flooding is not happening and may not happen — this is a heads-up to prepare and stay informed.
- Flood Advisory — Flooding is expected or occurring but is not severe enough for a warning — typically nuisance flooding of low-lying roads and poor-drainage areas.
- Flood Warning — Flooding is imminent or already happening. Take action to protect life and property in the affected area.
- Flash Flood Warning — Rapid, sudden flooding is imminent or occurring — often within minutes. Move to higher ground immediately; do not wait to see water.
In the most extreme cases the Weather Service may issue a flash flood emergency. It is rare and signifies a severe threat to human life with catastrophic damage occurring or imminent.
Watch versus warning, in one line
Watch = be ready. Warning = do something now. The distinction is the same one used for tornadoes and severe thunderstorms: a watch describes conditions that could produce the hazard, a warning means the hazard is happening or about to.
What to do when one is issued
Follow the guidance from the National Weather Service and your local emergency management agency — they issue the alerts and know the local risk. The universal rule in every flood alert is never drive or walk into floodwater: most flood deaths happen in vehicles, and it is impossible to judge depth or whether the road beneath is intact.
How this relates to gauge readings
Alerts and gauges are complementary. Alerts are official and cover areas; gauges are measurements at fixed points. IsItFlooding shows the gauge side — comparing live readings with the flood stage published for each gauge — which is useful for watching a specific river. It is not a substitute for official warnings, and it should never be used to decide whether it is safe to stay or travel.
Frequently asked questions
What is the difference between a flood watch and a flood warning?
A flood watch means conditions are favourable for flooding and you should prepare — it may not happen. A flood warning means flooding is imminent or already occurring and you should act. Watch is 'be ready'; warning is 'do something now'.
What is a flood advisory?
A flood advisory sits below a warning. It means flooding is expected or occurring but is not severe enough to threaten life or major property — typically water over low-lying roads or in poor-drainage areas. It still means take care, especially when driving.
How is a flash flood warning different?
A flash flood warning covers rapid flooding that can develop within minutes, usually from intense rainfall or a dam or levee failure. It is the most urgent routine flood alert, and the correct response is to move to higher ground immediately rather than wait for visible water.
Who issues flood watches and warnings?
The National Weather Service issues them for specific areas and river forecast points. Local emergency management agencies then act on them with evacuations, road closures, and shelter operations.
Can a river be above flood stage without a warning?
It can happen briefly, since warnings are issued for forecast points and areas rather than for every individual gauge. Treat a gauge above its flood stage as a real signal, and always follow official National Weather Service alerts for your area.
Related
What does flood stage mean · Why is the river rising · Live river levels near you