Extreme Heat

What qualifies as “extreme heat?” Extreme heat is a period of high heat and humidity with temperatures above 90 degrees for at least two or three days. 

Extreme heat can:

  • Occur quickly and without warning.
  • Present a greater risk for older adults, children and those who are sick or overweight.
  • Increase with humidity, as measured on a heat index.
  • Force your body to work extra hard to maintain a normal temperature, which can lead to death. Extreme heat is responsible for the highest number of annual deaths among all weather-related hazards.


There are a few things you can do to prepare in advance for a heat wave and extreme heat:

  1. Try to keep your home cool. Use shades or drapes, window reflectors to reflect heat back outside, insulation to keep heat out, and a powered attic ventilator or attic fan. Install weather-stripping on doors and windows and window air conditioners with insulation around them, if needed.
  2. Learn to recognize the signs of heat illness
  3. Keep plenty of bottled water at home. The body absorbs room temperature water more easily than cold water, so storing extra water for your family and guests is a good idea in the summer.

Stay Alert

It’s important to understand the difference between a heat watch vs warning, as defined by the National Weather Service: 

  • Excessive Heat Watch: issued when conditions are favorable for an excessive heat event in the next 24 to 72 hours.
  • Excessive Heat Warning: issued within 12 hours of the onset of extremely dangerous heat conditions. 
  • Heat Advisory: issued within 12 hours of the onset of dangerous heat.  
  • Excessive Heat Outlooks: issued when the potential exists for an excessive heat event in the next 3-7 days.

It’s also helpful to know the following terms about extreme heat:

  • Heat Wave: a period of abnormally hot weather generally lasting more than two days. Heat waves can occur with or without high humidity. 
  • Heat Index: a measure of how hot it feels when relative humidity is factored in with the actual air temperature. Exposure to full sunshine can increase the heat index by 15 degrees. 
The National Weather Service heat index chart.
  • Heat Cramps: muscular pains and spasms due to heavy exertion. Heat cramps may be the first signal that the body is having trouble with heat.
    • Signs: Sudden development of muscle pains or spasms in the stomach, arms, or legs.
    • Actions: Go to a cooler location. Remove excess clothing. Take sips of cool sports drinks with salt and sugar, unless there are complaints of nausea. Seek immediate medical attention if cramps last more than an hour. 
  • Heat Exhaustion: typically occurs when people exercise heavily or work in a hot, humid place where body fluids are lost through heavy sweating. Blood flow to the skin increases, causing blood flow to decrease to the vital organs. This results in a form of mild shock. If not treated, the victim’s condition will worsen. Body temperature will keep rising and the victim may suffer heat stroke.
    • Signs: Heavy sweating, paleness, muscle cramps, tiredness, weakness, dizziness, headache, nausea or vomiting, and fainting.
    • Actions: Go to an air-conditioned place and lie down. Loosen or remove clothing. Take a cool bath, shower or use cold compresses. Take sips of cool sports drinks with salt and sugar. Seek immediate medical attention if the person vomits, symptoms get worse or last more than an hour. 
  • Heat Stroke (also called Sun Stroke): a life-threatening condition. The victim’s temperature control system, which produces sweating to cool the body, stops working. The body temperature can rise so high that brain damage and death may result if the body is not cooled quickly.
    • Signs: Extremely high body temperature (above 103 degrees) indicated by an oral thermometer; red, hot, and dry skin with no sweat; rapid, strong pulse; dizziness; confusion; and unconsciousness.
    • Actions: Call 9-1-1 or get the person to a hospital immediately. Delay can be fatal. Do NOT give fluids. Cool down with whatever methods are available until medical help arrives.
The differences between heat exhaustion and heat stroke.

During an Extreme Heat Event

 If you are under an extreme heat warning:

  1. Find air conditioning. Libraries, shopping malls, and community centers can provide a cool place to take a break from the heat. If you’re outside, find shade. Find places in your community where you can go to get cool if your home doesn’t have air conditioning.
  2. Avoid strenuous and high-energy activities. Slow down during the hottest part of the day and stay indoors as much as possible.
  3. Wear light clothing. Wear a hat wide enough to protect your face and loose, light-colored clothing.
  4. Limit exposure to the sun. The sun is most powerful between 10 am and 4 pm.
  5. Use sunscreen. Apply it at least 20 minutes before going outside. 
  6. Drink plenty of fluids. If you or someone you care for is on a special diet, ask a doctor what would be best. The body absorbs room temperature water more easily than cold water. Avoid caffeinated and alcoholic drinks.
  7. Watch for heat cramps, heat exhaustion and heat stroke. Check yourself, family members, and neighbors for signs of heat-related illness.
  8. Never leave people or pets in a closed car, even for a few minutes. This is especially important for infants and seniors.
  9. Do not use electric fans when the temperature outside is more than 95 degrees. You could increase the risk of heat-related illness. Fans create air flow and a false sense of comfort, but do not reduce body temperature. They exhaust hot air from rooms or draw in cooler air. Do not direct the flow of air from electric fans toward yourself when the room temperature is higher than 90 degrees. The dry blowing air will dehydrate you faster.
There are distinct symptoms and first aid for each type of heat-related illness.

Alert Systems

Using alert systems is crucial to being informed before and during extreme heat events, just as with any other disaster. Our alert systems page has resources for a number of alert options.

Local Risks

History of extreme heat in Williamson County

A significant portion of Middle Tennessee suffers from events of extreme heat. Williamson County is strongly agricultural and highly populated. If an incident of extreme heat were to occur, economic and life safety issues may occur. It can also cause shock and put stress on plants and animals.

Prolonged periods of heat challenge the county’s infrastructure, residents, commuters and visitors. Higher temperatures lead to increased energy and water usage. In Williamson County, electrical demand soars during periods of “peak usage”, between 10 a.m. and 2 p.m. in commercial areas and between 7 p.m. and 11 p.m. in residential areas. Increased demand strains the county’s electrical distribution systems and may result in power disruptions that can last a few hours, days or weeks. The elderly, people with medical problems or those who are taking certain medications are particularly at risk because they may not be able to adequately keep cool using air conditioners or fans. 

In addition to increased electrical demand, extreme heat can result in lower water pressure due to illegal operation of fire hydrants, increased demand for water or pump failure due to loss of electricity. This situation can hamper the county’s fire and rescue suppression capabilities. 

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