The National Weather Service (NWS) uses a specific system of alerts to communicate potential weather danger and guide the public in making safety decisions. Confusion between an Advisory, a Watch, and a Warning can lead to dangerous inaction or unnecessary panic. This terminology is designed to clearly convey the level of risk and the necessary public response for a wide variety of weather events, from freezing rain to severe thunderstorms. Understanding the distinct meaning of each term is the first step in protecting life and property when hazardous weather approaches.
Understanding the Alert Hierarchy
A Watch is significantly more serious than an Advisory, but less severe than a Warning. The NWS employs a clear three-tiered severity hierarchy: an Advisory represents the lowest level of threat, a Watch indicates a medium or potential threat, and a Warning signifies the highest level of danger. This framework is determined by two primary factors: the expected severity of the weather event itself and the timing of its arrival.
The Advisory: Caution for Minor Threats
An Advisory is issued when a hazardous weather event is expected to cause significant inconvenience or could pose a minor threat if caution is not exercised. The weather conditions associated with an Advisory are generally not life-threatening and do not meet the criteria for a Watch or Warning. The required public action is primarily one of caution and increased awareness to mitigate minor risks. Specific examples include a Dense Fog Advisory, issued when visibility is expected to drop to one-quarter mile or less, or a Wind Advisory, issued for sustained winds between 31 and 39 miles per hour. During these events, the suggested response is to exercise situational awareness, such as driving slowly or securing loose outdoor objects.
The Watch: Conditions are Favorable
A Watch means that conditions are favorable for a particular severe weather event to develop in or near a specified area, but the event is not yet occurring or imminent. This alert provides the public with several hours of lead time to prepare for a potential threat. A Severe Thunderstorm Watch or a Tornado Watch typically covers a large geographical area and is issued for a duration of four to eight hours. The appropriate public response during a Watch is active preparation and monitoring. This includes identifying a safe room or shelter location, checking emergency supplies, and staying informed through local media and weather alerts.
The Warning: Danger is Imminent
A Warning represents the most serious level of alert, signifying that a severe weather event is either occurring or is about to occur in the specified area. The threat is considered life-threatening and requires immediate action to protect life and property. Warnings are highly localized, often issued for specific counties, and cover a much shorter time frame than a Watch. For example, a Tornado Warning is typically issued for about 30 minutes when a tornado has been sighted or indicated by Doppler radar. Similarly, a Flash Flood Warning means that dangerous flash flooding is already happening or will begin very soon, necessitating a move to higher ground immediately.