Weather alerts issued by meteorological services, such as the National Weather Service (NWS), communicate the potential and severity of hazardous weather conditions. Among the three main tiers of public notifications, an advisory represents the least severe level of alert. It is essentially a heads-up that conditions are occurring or are highly likely to occur. These conditions will cause a significant inconvenience or hazard if proper caution is not taken. The purpose of an advisory is to raise public awareness and encourage minor behavioral adjustments.
The Definition and Criteria of an Advisory
An advisory is issued when a hazardous weather or hydrologic event is occurring, imminent, or likely, but does not meet the criteria for a more urgent warning. Forecasters typically have an 80% or greater confidence that the specified conditions will materialize. These conditions are considered less serious than those that pose an immediate, life-threatening risk. The primary impact of advisory-level weather is significant inconvenience, rather than widespread destruction.
Specific criteria determine when an advisory is necessary, and these thresholds vary depending on the type of weather event. For example, the NWS issues a Wind Advisory for sustained wind speeds between 31 and 39 miles per hour, or for frequent gusts between 46 and 57 miles per hour. A Dense Fog Advisory is activated when widespread fog is expected to reduce visibility to one-quarter mile or less for two hours or more. These specific metrics separate an advisory from both lesser and more severe alert levels.
For winter weather, a Winter Weather Advisory is issued when snow, sleet, or freezing rain is expected to cause substantial travel inconvenience but falls below warning accumulation thresholds. This typically involves snow accumulations of 2 to 4 inches, or any amount of freezing rain that causes slippery road surfaces. The advisory level signifies that while the weather is hazardous, exercising extra caution should prevent the situation from becoming dangerous. Communication focuses on potential impacts like slick roads, minor tree damage, and unsecured objects blowing around.
Understanding the Alert Hierarchy
The National Weather Service utilizes a three-tiered system—Watch, Advisory, and Warning—to communicate the escalating threat level of hazardous weather. A Watch is the lowest tier, signaling that conditions are favorable for a hazardous event to develop, usually within the next 12 to 48 hours. It means the weather is possible, and the public should be prepared to act if the threat increases. The watch is a preparatory notice that allows people to make a plan while the occurrence, location, or timing remains uncertain.
The Advisory occupies the middle tier and represents a higher certainty that a hazardous event will occur, requiring the public to exercise caution. This alert level is issued for conditions that present a threat of inconvenience or can become dangerous if ignored. It serves as a direct instruction to modify behavior and increase awareness of the existing hazard.
A Warning is the highest and most urgent tier, indicating that a severe weather event is already occurring or is imminent. Warnings pose an immediate threat to life and property. When a warning is issued, conditions are dangerous, and people must take immediate, protective action to ensure their safety. This level is reserved for the most severe weather, such as a tornado or a flash flood.
Practical Safety Measures During an Advisory
When an advisory is in effect, the appropriate public response is to acknowledge the hazard and make minor modifications to daily plans. The required actions are generally less severe than sheltering in place. For a Wind Advisory, homeowners should secure lightweight outdoor items such as trash cans, patio furniture, and trampolines, which could otherwise become projectiles. Drivers of high-profile vehicles must exercise increased caution, anticipating strong crosswinds that can make steering difficult.
If a Dense Fog Advisory is issued, drivers need to slow down significantly, increase the following distance between vehicles, and use low-beam headlights. Traveling is not advised against entirely, but it requires careful adjustment to operating procedures. Similarly, a Winter Weather Advisory should prompt individuals to check road conditions before traveling and allow extra time for their commute.
Staying informed about changing conditions through reliable weather sources is important during any advisory. This allows individuals to quickly determine if the advisory is upgraded to a warning, requiring more immediate and protective actions. The focus remains on exercising prudent judgment and adjusting activities to minimize the risk of inconvenience or accident. Advisories emphasize awareness and minor modifications to plans, not a complete halt to normal activity.