Natural Disasters – Extreme Heat

Extreme Heat Fact Sheet
Summer heat waves are the biggest weather-related killers in Wisconsin for the past 50 years, far exceeding tornado and other storm-related deaths. In 1995, two major killer heat waves affected most of Wisconsin resulting in 154 heat-related deaths and over 300 heat-related illnesses.

Wisconsin can be seriously affected by severe heat, and it is essential that people are aware of the dangers of heat waves and the protective actions they can take to protect themselves.


Know the Terms

Heat Wave – Prolonged period of excessive heat, often combined with excessive humidity.

Heat Index – A number in degrees Fahrenheit (F) that tells how hot it feels when relative humidity is added to the air temperature. Exposure to full sunshine can increase the heat index by 15 degrees.

Heat Cramps – Muscular pains and spasms due to heavy exertion. Although heat cramps are the least severe, they are often the first signal that the body is having trouble with the heat.

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.

Heat 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.

Sun Stroke – Another term for heat stroke.


National Weather Service Heat Wave Program in Wisconsin

Outlook Statement – Issued 2 to 7 days in advance of when Heat Advisory or Excessive Heat Warning conditions are anticipated. Issued as a Hazardous Weather Statement (HWO). Broadcasted on NOAA Weather Radio All Hazards, and posted on NWS websites.

Heat Advisory – Issued 6 to 24 hours in advance of any 24-hour period in which daytime heat index (HI) values are expected to be 105-110 for 3 hours or more and nighttime HI values will be 75 or higher. For west central and northwest Wisconsin, numbers are 105-114 and 80, respectively.

Excessive Heat Watch – Issued generally 12 to 48 hours in advance of any 24-hour period in which daytime heat index (HI) values are expected to exceed 110 for 3 hours or more and nighttime HI values will be 80 or higher. For west central and northwest Wisconsin, numbers are 115 or higher, and 80 or higher, respectively.

Excessive Heat Warning – Issued 6 to 24 hours in advance of any 24-hour period in which daytime heat index (HI) values are expected to exceed 110 for 3 hours or more and nighttime HI values will be 80 or higher. For westcentral and northwest Wisconsin, numbers are 115 or higher, and 80 or higher, respectively.


What to do during periods of extreme heat:

Never leave children, disabled persons, or pets in a parked car – even briefly. Temperatures in a car can become life threatening within minutes.

Keep your living space cool. Cover windows to keep the sun from shining in. If you don’t have an air conditioner, open windows to let air circulate. When it’s hotter than 95 degrees, use fans to blow hot air out of the window, rather than to blow hot air on to your body. Basements or ground floors are often cooler than upper floors.

Slow down and limit physical activity. Plan outings or exertion for the early morning or after dark, when temperatures are cooler.

Drink plenty of water and eat lightly. Don’t wait for thirst, but instead drink plenty of water throughout the day. Avoid alcohol or caffeine and stay away from hot, heavy meals.

Wear lightweight, loose-fitting, light colored clothing. Add a hat or umbrella to keep your head cool…and don’t forget sunscreen!

Don’t stop taking medication unless your doctor says you should. Take extra care to stay cool, and ask your doctor or pharmacist for any special heat advice.

Taking a cool shower or bath will cool you down. In fact, you will cool down faster than you will in an air-conditioned room! Also, applying cold wet rags to the neck, head and limbs will cool down the body quickly.

Make sure pets and livestock are protected. Be sure they have access to plenty of water and a shady place to rest. Keep pets indoors and never leave them inside a parked vehicle.


People at higher risk of a heat related illness include:

  • Older adults
  • Infants and young children
  • People will chronic heart or lung problems
  • People with disabilities
  • Overweight persons
  • Those who work outdoors or in hot settings
  • Users of some medications, especially those taken for mental disorders,
  • Movement disorder, allergies, depression, and heart or circulatory problems
  • People that are isolated who don’t know when or how to cool off – or when to call for help

Additional Resources
Wisconsin Extreme Heat Toolkit
Extreme Heat Fact Sheet
National Weather Service heat safety tips
Wisconsin Emergency Management Heat Awareness packet