Weather Watches, Warnings and Advisories: What’s the Difference?

Your phone lights up with a weather alert. Is it something you need to act on now, something to keep an eye on, or simply a heads-up that conditions could make travel difficult?

The words watch, warning and advisory aren't interchangeable. In the United States, the National Weather Service uses different types of alerts to communicate both the likelihood and seriousness of hazardous weather.

The easiest distinction to remember is this: a watch means hazardous weather is possible, while a warning means it is occurring, imminent or expected and you should take appropriate action. An advisory generally means hazardous weather is expected but at a level that is less severe than conditions requiring a warning—although it can still cause significant inconvenience or danger.

Understanding those differences makes all those phone notifications much more useful.

What Does a Weather Watch Mean?

A watch means conditions are favorable for a particular type of hazardous weather, but it isn't certain that the event will occur at your exact location. Think of a watch as advance notice to pay attention and be prepared.

A severe thunderstorm watch, for example, means atmospheric conditions are favorable for severe thunderstorms to develop in or near the watch area. It doesn't mean a severe thunderstorm is currently bearing down on your house. Summer thunderstorms can be surprisingly localized, with one area receiving a downpour while another nearby gets very little rain.

Similarly, a tornado watch means conditions could produce tornadoes. You don't necessarily need to take shelter immediately, but you should know where you would go if a warning is issued and keep track of changing conditions.

Watches often cover fairly large areas because forecasters can identify a region where the ingredients for dangerous weather are coming together before they know precisely where individual storms will develop.

What Does a Weather Warning Mean?

A warning is more urgent.

Warnings are issued when hazardous weather is occurring, imminent or expected. Depending on the type of warning, the threat may have been detected by radar, observed by trained spotters or indicated strongly enough by other evidence that people in the affected area need to act. Weather radar can reveal where precipitation is falling and help estimate how heavy it is, making it an important tool for tracking developing storms.

If a tornado warning is issued for your location, for example, the time for simply watching the weather has passed. You should move to an appropriate safe location.

A severe thunderstorm warning means a storm meeting severe criteria is occurring or imminent in the warned area. A flash flood warning means dangerous flooding is occurring or expected soon.

Warnings also tend to be more geographically specific than watches. A large portion of a state might be under a tornado watch while only the communities in the path of a particular dangerous storm are placed under a tornado warning.

A useful way to remember it is: watch for the possibility; respond to the warning.

So What Is a Weather Advisory?

An advisory generally covers hazardous weather that isn't expected to reach the severity required for a warning but could still cause problems if you aren't prepared.

Winter weather is a familiar example. A winter weather advisory may be issued when snow, sleet or freezing rain is expected to make roads and sidewalks hazardous even though the event isn't expected to meet warning-level criteria. Which type of precipitation reaches the ground depends on the temperatures it encounters on the way down—one reason rain, snow, sleet and freezing rain can occur under very different conditions.

Other advisories can cover conditions such as wind, dense fog, freezing fog or certain coastal hazards, depending on the situation and location.

“Advisory” shouldn't be interpreted as “nothing to worry about.” A few inches of snow may not qualify for a winter storm warning in a particular area, but it can still make a commute dangerous. Dense fog may not be a major storm, but driving through it can be hazardous.

The alert level helps describe the expected hazard. Your own circumstances still matter.

A Severe Thunderstorm Watch vs. Warning

Thunderstorms provide one of the clearest examples of how the system works.

Imagine it's a hot, humid summer afternoon. Forecasters see that the atmosphere contains the ingredients necessary for powerful thunderstorms, but no one knows exactly where the strongest storms will develop. A severe thunderstorm watch may be issued across a broad region.

Later, radar shows a storm intensifying and moving toward several communities. If it meets the appropriate criteria, the National Weather Service may issue a severe thunderstorm warning for the area in its path.

People elsewhere may remain under the watch but never receive a warning at all.

That's not a failed watch. The purpose of the watch was to alert the larger region that severe storms were possible and that people should be prepared if one developed nearby. In fact, rainfall can vary dramatically across surprisingly short distances, especially with scattered summer thunderstorms.

What About Flood Watches and Warnings?

Flood terminology follows the same general idea, although flooding can be particularly complicated because different types develop at very different speeds.

A flood watch means conditions are favorable for flooding. Heavy rain may be expected, soils may already be saturated or rivers may be running high enough that additional rainfall could cause problems.

A flood warning means flooding is occurring or expected. A flash flood warning is particularly urgent because flash flooding can develop quickly and produce rapidly moving water in streams, roads, low-lying areas and normally dry locations.

Rainfall totals alone don't determine whether flooding will occur. An inch of rain falling gradually on dry ground can have a very different effect from an inch falling in 20 minutes onto saturated soil.

Where the rain falls, how quickly it falls and what happened in the days before the storm can all matter. Some rain soaks into the soil and eventually becomes groundwater, while intense rainfall can arrive faster than the ground can absorb it, increasing runoff and flooding.

Winter Weather Has Its Own Set of Alerts

Winter alerts can seem especially confusing because snow, sleet, freezing rain, wind and extreme cold can occur in different combinations.

A winter storm watch generally means significant winter weather is possible. As the event gets closer and forecasters become more confident, that watch may be replaced by a warning or advisory depending on the expected severity.

A winter storm warning means significant snow, sleet or ice is expected or occurring and is likely to create substantial impacts. A winter weather advisory generally covers less severe accumulations that can nevertheless make travel hazardous.

You may also see more specific alerts for hazards such as ice storms, blizzards or extreme cold. The exact criteria can vary by location because the same weather can have very different impacts in different parts of the country.

Six inches of snow means something quite different in Buffalo than it does in a city that rarely sees snow.

Why Doesn't Every Storm Produce an Alert?

Bad weather and hazardous weather aren't necessarily the same thing.

A thunderstorm can produce heavy rain, gusty winds and plenty of lightning without meeting the criteria for a severe thunderstorm warning. A snowfall can make roads slippery without becoming a major winter storm. A windy day may be unpleasant without reaching the level required for a wind-related alert.

National Weather Service alerts are intended to identify conditions that meet particular hazard and impact thresholds, not to provide a notification every time the weather becomes unpleasant.

That's why it's still useful to read the regular forecast even when there are no watches or warnings in effect.

Why Do Alerts Sometimes Change Quickly?

Weather alerts change because the weather changes and new information continually arrives.

A watch issued in the morning may be followed by several warnings that afternoon as individual storms develop. A winter storm watch may become a warning if confidence in significant snow increases—or an advisory if the expected storm becomes weaker.

Radar, satellites, weather stations, weather balloons and other observations continually provide new information. Forecast models are updated, and forecasters adjust alerts as the location, timing and severity of a threat become clearer. Modern forecasting has come a long way from the days when people relied primarily on observations of the sky and changes in local conditions; the history of weather forecasting shows how dramatically those tools have changed.

An alert changing doesn't necessarily mean the earlier forecast was wrong. Often it means the uncertainty has narrowed. And that uncertainty increases the farther into the future we look, which is why weather forecasts become less certain as the forecast period gets longer.

Pay Attention to the Location, Not Just the Alert Name

When an alert appears on your phone, the headline is only part of the information.

Check whether your location is actually within the affected area, when the alert begins and ends, what hazard is expected and what actions are recommended. This is especially important with thunderstorms and flash flooding, where warning areas can be relatively small and conditions can change quickly.

It's also one reason the weather you experience at home may not perfectly match a forecast or app. Rainfall can vary from one neighborhood—or even one yard—to another, particularly during localized storms.

It's also worth having more than one way to receive important warnings. Cellphone emergency alerts are useful, but weather radios, local broadcasters and official weather sources can provide additional information, particularly during widespread power or communications outages.

Watch, Warning or Advisory: What Should You Remember?

You don't need to memorize every type of weather alert to make sense of the system.

When you see a watch, pay attention and be prepared because hazardous weather is possible. When you see a warning for your location, the threat is occurring, imminent or expected, so follow the recommended safety instructions. An advisory means conditions may be less severe but can still cause hazards and disrupt normal activities.

And remember that the alert describes more than the weather itself. It is trying to communicate the risk that weather poses to people in a particular place at a particular time.