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Scale of threat levels

for South Central and Southeast Wisconsin
Excessive Heat Threat
Hazard Map Threat Levels Safety & Impact
The "Excessive Heat Hazard Map" depicts the local threat of expected warm season weather conditions for specified areas.  It is largely based on highest maximum temperature and the effects of humidity.

Excessive Heat Threat Level

Threat  Level Descriptions

Extreme

"An Extreme Threat to Life and Property from Excessive Heat."

An extreme likelihood (36% or greater probability) that for any 24-hour period the heat index will exceed 1100 F for 3 hours or more during the day and stay at or above 800 F at night for a defined area.

High

"A High Threat to Life and Property from Excessive Heat."

A high likelihood (26% to 35% probability) that for any 24-hour period the heat index will exceed 1100 F for 3 hours or more during the day and stay at or above 800 F at night for a defined area.

Moderate

"A Moderate Threat to Life and Property from Excessive Heat."

A moderate likelihood (16% to 25% probability) that for any 24-hour period the heat index will exceed 1100 F for 3 hours or more during the day and stay at or above 800 F at night for a defined area.

Low

"A Low Threat to Life and Property from Excessive Heat."

A low likelihood (6% to 15% probability) that for any 24-hour period the heat index will exceed 1100 F for 3 hours or more during the day and stay at or above 800 F at night for a defined area.

Very Low
"A Very Low Threat to Life and Property from Excessive Heat."

A very low likelihood (2% to 5% probability) that for any 24-hour period the heat index will exceed 1100 F for 3 hours or more during the day and stay at or above 800 F at night for a defined area.
Non-Threatening
" No Discernable Threat to Life and Property from Excessive Heat."

Warm season weather conditions are non-threatening.   

Note: Warm season weather conditions become hazardous when the associated heat is considered to be "excessive" relative to the human body's normal temperature of 98.6 degrees (F).

This occurs when heat indices reach or exceed 99 degrees (F).  At this point, heat may begin to build within the body.  In situations when the humidity is very low, the heat index is approximately the same as the actual ambient temperature.

Your body may quickly lose fluids as sweat (the body's natural cooling mechanism) readily evaporates; dehydration can rapidly occur.  In situations when the humidity is very high, body sweat may be slower to evaporate and therefore excess heat can not be efficiently removed causing a person to quickly overheat.

Heat Index Possible heat disorders for people in higher risk groups
1300 F or higher Heat Stroke/Sun Stroke highly likely with continued exposure
1050 F - 1300 F Sun Stroke, heat cramps or heat exhaustion likely with prolonged exposure and/or physical activity.
900 F - 1050 F Sun Stroke, heat cramps and heat exhaustion possible with prolonged exposure and/or physical activity.
800 F - 900 F Fatigue possible with prolonged exposure and/or physical activity.

Determining Likelihood

  • NOAA's National Weather Service
  • Milwaukee/Sullivan, WI Weather Forecast Office
  • N3533 Hardscrabble Road
  • Dousman, WI 53118
  • 414-744-8000
  • Page Author: MKX Webmaster
  • Web Master's E-mail: w-mkx.webmaster@noaa.gov
  • Page last modified: 2-Nov-2005 10:23 PM UTC
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