The National Weather Service (NWS) uses a tiered alert system to communicate the potential for severe weather, including floods, to the public. Understanding the hierarchy of these messages is necessary for knowing the appropriate actions to take when water hazards are possible. Differentiating between a Flood Watch, a Flood Advisory, and a Flood Warning determines the level of caution and action that is required for personal safety.
The Scope of a Flood Advisory
A Flood Advisory is issued by the National Weather Service when a specific weather event is expected to cause minor flooding that is generally not life-threatening. The advisory acts as a notice to “be aware” of potential hazards that may cause significant inconvenience or a public nuisance.
This type of localized flooding is often caused by heavy rainfall over a short duration that overwhelms drainage systems in urban areas or leads to minor overflow of small creeks and streams. Water pooling in low-lying areas, underpasses, and streets with poor drainage are common results of an advisory-level event. While property damage is typically minimal or non-existent, the conditions still pose a risk if caution is not exercised, especially for drivers.
How Advisories Differ from Watches and Warnings
The National Weather Service employs three distinct terms—Watch, Advisory, and Warning—to categorize the severity and immediacy of a flooding threat. This system provides a clear, progressive scale of risk that guides public response.
The lowest tier is the Flood Watch, which is issued when conditions are favorable for flooding to occur, meaning a threat is possible but not guaranteed. The Flood Watch is a signal to “be prepared” because the circumstances are ripe for a flood event, often covering a larger geographical area and a longer time frame than an advisory.
A Flood Advisory occupies the middle tier, signifying that a minor, nuisance-level flood is expected or is already happening. Advisories are typically issued for smaller, localized events that cause inconvenience rather than posing an immediate, widespread danger to life and property.
The highest level of alert is the Flood Warning, reserved for situations where severe flooding is imminent or already occurring. A Warning signals an immediate threat to life and property, requiring the public to “take action” without delay. This distinction prompts evacuation orders and advises moving to higher ground because the floodwater levels will be high enough to cause significant structural damage and present a clear danger.
Essential Safety Measures During Localized Flooding
When a Flood Advisory is in effect, the most immediate action is to monitor local weather reports and tune into official channels for updates, as conditions can change rapidly. People should actively avoid known flood-prone locations, such as low-lying roads, underpasses, and areas near drainage ditches. Being alert to the surroundings is important, especially when driving, because water depth can be deceptive, hiding hazards like washed-out roadbeds or sharp debris.
The single most important safety message during any flood event is the directive to “Turn Around, Don’t Drown.” It takes surprisingly little moving water to create a dangerous situation; as little as six inches of fast-moving water is enough to knock an adult off their feet and sweep them away.
Driving through floodwaters is especially hazardous. Twelve inches of moving water is enough to float many small cars, while eighteen to twenty-four inches can carry away larger trucks. If a vehicle stalls in water, occupants should abandon it immediately and move to higher ground. It is prudent to prepare for a possible escalation by having an emergency kit ready with essential supplies, in case the Advisory is upgraded to a Warning.