Hot weather safety and heat index chart

Published: Jun. 9, 2017 at 10:48 PM CDT|Updated: Apr. 14, 2021 at 11:17 AM CDT
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Summer heat kills more people each year than floods, lightning, tornadoes and hurricanes. The only deadlier weather condition is the cold of winter.

A heat wave is usually defined as three consecutive days with high temperatures above 90 degrees Fahrenheit. Though days of heat can take their toll on our reserves, even a single day of hot weather can be dangerous if we try to do too much or are confined to an area that becomes too hot.

Hot weather feels even hotter when its humid. Moisture in the air prevents perspiration from evaporating, which is how the body cools itself. Below is the Heat Index Chart, which shows how hot the weather feels to your body as the relative humidity (RH) rises.

Effects of the Heat

80 to 90 degrees

Fatigue possible with prolonged exposure and/or physical activity.

90 to 105 degrees

Sunstroke, heat cramps, and/or heat exhaustion possible with prolonged exposure and or physical activity.

105 to 130 degrees

Sunstroke, heat cramps, and/or heat exhaustion likely, and heatstroke possible with prolonged exposure and/or physical activity.

130 degrees and higher

Heat stroke/sunstroke highly likely with continued exposure.

Beating the Heat

The most obvious: Stay indoors or out of the sun. Run air-conditioning, or fans if they cool the air (circulating a hot breeze can be worse than no breeze). Otherwise enjoy public, air-conditioned places such as shopping malls.

Drink more water or juice. Avoid drinks with caffeine, carbonation. Also avoid alcohol, which dries you out and reduces your ability to recognize signs of heat stress.

Eat less protein and other foods that increase your metabolism.

Wear light-colored, loose-fitting clothes.

Avoid strenuous activity including running, bicycling, and yard work.

Check on the elderly, who are most susceptible to heat stress.

Check on children, who may be too young-- or simply having too much fun-- to recognize the signs of heat stress.


Heat Cramps

What it is: Painful spasms, typically in the legs or abdomen.

What to do: Apply firm pressure to cramping muscles, or gently massage to relieve spasm. Give sips of water. If nausea occurs, discontinue water.

Heat Exhaustion

What it is: Heavy sweating, weakness, skin cold, pale, and clammy. Pulse thready. Normal temperature possible. Fainting and vomiting.

What to do: Get victim out of the sun. Lay down and loosen clothing. Apply cool, wet cloths. Fan, or move victim to air-conditioned room. Give sips of water. If nausea occurs, discontinue water. If vomiting continues, seek immediate medical attention.

Heat Stroke/Sunstroke

What it is: High body temperature (106 degrees F or higher). Hot dry skin. Rapid and strong pulse. Possible unconsciousness.

What to do: Heat stroke is a SEVERE MEDICAL EMERGENCY. Get emergency medical assistance or get the victim to a hospital IMMEDIATELY. Delay can be fatal. Until you can get medical help, move the victim to a cooler environment. Reduce body temperature with cold bath or sponging. Use extreme caution. Remove clothing, use fans and air-conditioners. If temperature rises again, repeat process. Do NOT give fluids.

Temperature (° F)
Note: Exposure to direct sunlight can increase heat index values up to 15° F

How hot it gets in a car

Elapsed time
Interior temp (° F)
0 70 75 80 85 90 95
10 89 94 99 104 109 114
20 99 104 109 114 119 124
30 104 109 114 119 124 129
40 108 113 118 123 128 133
50 111 116 121 126 131 136
60 113 118 123 128 133 138
More than 60 115 120 125 130 135 140


Source: Wisconsin Dept. of Agriculture, Trade and Consumer Protection