When meteorologists forecast a “potential for severe thunderstorms,” they communicate a calculated, elevated risk based on atmospheric conditions. This standardized terminology alerts the public to the possibility of dangerous weather. The phrase indicates that the necessary ingredients are present for storms to develop and reach severity thresholds that threaten life and property. Understanding this forecast is the first step in protecting yourself, as it signifies a time when heightened awareness and preparation are necessary.
Defining Severe Thunderstorm Criteria
A thunderstorm is classified as “severe” only when it meets specific, objective criteria, independent of the storm’s overall size or lightning frequency. The National Weather Service (NWS) defines a storm as severe if it produces any one of three distinct hazards.
The first criterion relates to straight-line wind gusts equal to or exceeding 58 miles per hour (about 93 kilometers per hour). Winds this strong are capable of causing significant damage, such as breaking off large tree branches, knocking down trees, or inflicting structural damage to buildings. These damaging winds are often a major source of power outages.
The second criterion is the presence of large hail, defined as hailstones with a diameter of 1 inch or larger. This size is roughly equivalent to the diameter of a quarter coin. Hail of this size can cause substantial property damage, including denting vehicles, cracking windshields, and damaging roofs and crops.
Finally, any thunderstorm that produces a tornado is automatically classified as severe, regardless of the accompanying wind speed or hail size. A storm only needs to satisfy one of these three conditions—damaging wind, large hail, or a tornado—to be labeled a severe thunderstorm.
Understanding Watches Versus Warnings
The communication of severe weather potential relies on a clear distinction between two primary alert types: the severe thunderstorm watch and the severe thunderstorm warning. These terms convey different levels of immediacy and required public response.
A Severe Thunderstorm Watch is issued when the atmospheric conditions are favorable for severe thunderstorms to develop in and near a defined area, often encompassing multiple counties or even states. A watch means that severe weather is possible, typically within the next four to eight hours. This alert signals the public to monitor the situation and be prepared to take action if the risk materializes.
Conversely, a Severe Thunderstorm Warning is the highest level of alert, indicating that severe weather is either imminent or already occurring. Warnings are issued based on radar indications or reports from trained spotters confirming that a storm is producing hail of one inch or greater, or winds of 58 miles per hour or more. This alert covers a much smaller, more specific geographic area. A warning demands immediate, life-saving action, as the danger is present and poses an imminent threat to life and property.
Practical Steps for Severe Weather Preparation
Responding effectively to the potential for severe thunderstorms requires a tiered approach, beginning with preparation when a watch is issued and escalating to immediate action during a warning. Preparation starts with creating a family communication plan that includes a designated emergency meeting place. This plan ensures that family members know how to reconnect if they are separated when a storm strikes.
It is helpful to identify a safe room within the home ahead of time, which should be a small, interior room on the lowest floor, such as a closet or bathroom, away from windows. This location provides the best protection from high winds and flying debris. Outside the home, secure or bring inside any loose objects, like patio furniture, trampolines, or decorations, as these can become dangerous projectiles in strong winds.
When a Severe Thunderstorm Warning is issued, the time for preparation ends, and immediate action is necessary. Move quickly to the pre-determined safe room or shelter, whether it is a basement or an interior, windowless space on the ground floor. If a basement is unavailable, staying as close to the center of the building as possible offers the most structural protection.
Once in the safe location, crouch low and use arms or a blanket to cover your head and body for protection against falling debris. Ensure that you have multiple ways to receive alerts, such as a battery-powered NOAA weather radio or mobile phone alerts, as power outages may disable standard television and internet access. Taking these steps when a warning is active significantly increases the chance of minimizing injury and property damage.