Extreme heat is a significant public health threat, and meteorological services use alerts to notify the public of dangerous conditions. A Heat Advisory is a formal notification issued by the National Weather Service (NWS) when high temperatures and humidity are expected to combine, posing a risk to health and safety. This alert triggers preventative actions to reduce heat-related illnesses. Recognizing the meaning of this alert and knowing the proper response safeguards yourself and others during oppressive heat.
Defining the Heat Advisory: Criteria and Purpose
A Heat Advisory is issued when dangerous conditions are expected but are not severe enough to meet the more extreme “Warning” criteria. This alert is typically issued 12 to 24 hours before the anticipated onset of the heat. The primary metric for determining this alert is the Heat Index, often called the “feels like” temperature, which accounts for both air temperature and relative humidity.
The Heat Index calculates how hot it feels because high humidity impairs the body’s ability to cool itself through sweat evaporation. Criteria vary based on local climate, but an Advisory is commonly issued when the Heat Index is expected to reach or exceed \(100^{\circ}\) Fahrenheit, or sometimes \(105^{\circ}\) Fahrenheit. The purpose is to alert vulnerable populations, such as the elderly, young children, and those with pre-existing health conditions, to the heightened risk of heat-related illness.
The National Weather Service Heat Alert Hierarchy
The Heat Advisory is part of a tiered system designed to communicate the severity and timing of extreme heat events. The least urgent alert is the Excessive Heat Watch, issued 24 to 72 hours in advance when conditions are favorable for extreme heat. A Watch provides lead time for communities to prepare for the possibility of dangerous heat, such as planning to suspend major outdoor activities.
The Heat Advisory is the next level, signifying that dangerous heat conditions are expected and require the public to take action. It indicates Heat Index values high enough to cause illness if precautions are not taken, but they fall short of the most severe threshold. The highest level is the Excessive Heat Warning, issued when extremely dangerous heat conditions are imminent or already occurring. A Warning indicates a significant threat to life and mandates the most stringent preventative measures, such as avoiding outdoor activities entirely.
Immediate Actions and Safety Protocols
When a Heat Advisory is issued, the focus shifts to preventative measures. Maintaining hydration is essential; drink water or non-alcoholic fluids, even before feeling thirsty. Adequate fluid intake is necessary because the body uses water to produce sweat for heat dissipation.
Strenuous outdoor activities should be reduced, postponed, or rescheduled to the coolest parts of the day, typically before 10 a.m. or after 4 p.m. If outdoor exposure is unavoidable, seek air-conditioned environments, such as public cooling centers, for significant portions of the day. Wearing lightweight, light-colored, and loose-fitting clothing helps manage heat by reflecting sunlight and allowing sweat to evaporate. Never leave children, the elderly, or pets unattended in a parked vehicle, as interior temperatures rise rapidly to life-threatening levels.
Recognizing and Responding to Heat Illnesses
Recognizing the symptoms of heat-related illness is important due to the increased risk signaled by a Heat Advisory. Heat exhaustion is characterized by heavy sweating, weakness, a rapid and weak pulse, and cool, pale, clammy skin. Symptoms also include muscle cramps, dizziness, nausea, or fainting.
If heat exhaustion is suspected, move the person to a cooler environment, loosen their clothing, and cool them with wet cloths or a cool bath. They should be given small sips of water, but if vomiting occurs or symptoms worsen, immediate medical attention is necessary. Heat stroke is a medical emergency occurring when the body’s temperature control system fails, often presenting with a body temperature of \(103^{\circ}\) Fahrenheit or higher, confusion, slurred speech, and a rapid, strong pulse. Skin may be hot and red, and may be either dry or damp.
A person showing signs of heat stroke requires an immediate call to 911 or local emergency services. While waiting for help, move the person to a cooler location and actively cool them with cold compresses or a cool bath.