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Heat Wave: A Major Summer Killer in Wisconsin

From the Warning Coordination Meteorologists at National Weather Service Offices servicing Wisconsin


  • Wisconsin normally doesn't experience many heat waves, and is better known for its cold, snowy winters.  However, killer heat waves have and will continue to affect the Badger State.

  • During the summer of 1995, two killer heat waves affected most of Wisconsin. Together, they resulted in 154 heat-related deaths and probably 300 to 400 heat-related illnesses.

    This makes the combined 1995 summer heat waves the biggest weather-related killers in Wisconsin for the past 50 years, far exceeding tornado deaths.

  • The 8-day heat wave in June 1995 claimed 11 lives, while the 3-day super heat wave of July 13-15 claimed 140 lives (70 directly related and 70 indirectly related).

    Most of the deaths occurred in the major urban centers of southeast Wisconsin, with the elderly and young being the highest risk groups.

  • July 1999 featured heat waves on the 4th and 5th, the 23rd through the 25th, and the 29th through the 31st.  Collectively, these heat waves were responsible for 20 deaths (12 directly and 8 indirectly).

  • Several heat waves from mid-July through early August 2001 claimed 15 fatalities (10 direct and 5 indirect) across Wisconsin.  Probably 300 or more were treated at hospitals for heat exhaustion.

    Temperatures topped out in the mid to upper 90s.  However, on August 7th, they topped out at 102 at Mt. Mary College in Milwaukee and 101 in Buffalo and Trempealeau counties.


  • Heat waves usually consist of high temperatures and high relative humidity. This combination makes it difficult for the human body to dissipate heat through the skin and sweat glands.

    Sweating will not cool the human body unless the water is removed by evaporation. High relative humidity consequently retards evaporation. Certain medications can also make it difficult for a person to sweat.

  • The National Weather Service (NWS) uses the "HEAT INDEX" as a measure of the combined affects of high temperatures and high relative humidity.

  • Research findings strongly suggest the HEAT INDEX (HI) values of 90 to 105 make sunstroke, heat cramps, and heat exhaustion possible with prolonged exposure and/or physical activity.

  • Research findings strong suggest that HI values of 105 to 130 degrees make sunstroke, heat cramps, and heat exhaustion likely with prolonged exposure and/or physical activity.

  • The NWS issues Heat Advisories when it expects daytime HIs to equal or exceed 105 for 3 hours or more while nighttime HIs equal or exceed 80 (75 for South-central and Southeast Wisconsin), for any 24-hour period.

  • The NWS issues Excessive Heat Warnings when it expects daytime HIs to equal or exceed 115 (110 for South-central and Southeast Wisconsin) for 3 hours or more while nighttime HIs equal or exceed 80 for any 24-hour period.

    The NWS may issue an "Excessive Heat Watch" 24 to 8 hours in advance of heat wave conditions.


  • Slow down (reduce outdoor activities)

  • Dress for summer (wear lightweight light-colored clothing)

  • Drink plenty of water or other non-alcohol fluids (check with your doctor if you are on medications or have a problem with fluid retention)

  • Spend more time in air conditioned places

  • If your home doesn't have air conditioning:

    • Spend some time in an air conditioned facility during the worst of the heat

    • Or sit in a bath tub containing cool water

    • Don't get too much sun (sunburn makes it more difficult to cool off)

Keep in mind that the young, elderly, people on medication, and people with weight or alcohol problems are at a greater risk during heat waves.  Certain medications may "turn off" the sweating mechanism in some people, thus making it very difficult for them to cool down by sweating.

Use common sense, and use the buddy system - frequently contact those individuals who are at a greater risk and help them obtain relief from the heat and humidity.

  • Listen to NOAA Weather Radio (exit DHS), commercial TV or radio, or cable TV for the latest forecasts and heat index values.

Last Updated: July 18, 2013