The National Weather Service (NWS) has issued a variety of heat warnings and advisories for Illinois this week. The combination of temperatures in the upper 90s and high levels of humidity mean a greater risk of heat-related illnesses and death.
One measure that combines both the effects of temperature and humidity is the heat index. Explanations of the heat index can be found on Wikipedia and NWS. Below is a chart showing the heat index for a given temperature and relative humidity. If you like to do your own calculations, here is the NWS heat index calculator.
While the heat index incorporates relative humidity to give a better idea of what the temperature feels like, there are some important underlying assumptions. It assumes a person who is 5′ 7″, 147 lbs, walking at 3 mph, wearing long pants and a short-sleeve shirt, in the shade with a light breeze. It is estimated that working out in the sun would increase the heat index by 15°F.
Here are some resources to consider for monitoring the heat and what to do during the current heat wave:
| HEAT INDEX |
|
RELATIVE HUMIDITY (%) |
| Temp. |
40 |
45 |
50 |
55 |
60 |
65 |
70 |
75 |
80 |
85 |
90 |
95 |
100 |
| 110 |
136 |
|
|
|
|
|
|
|
|
|
|
|
|
| 108 |
130 |
137 |
|
|
|
|
|
|
|
|
|
|
|
| 106 |
124 |
130 |
137 |
|
|
|
|
|
|
|
|
|
|
| 104 |
119 |
124 |
131 |
137 |
|
|
|
|
|
|
|
|
|
| 102 |
114 |
119 |
124 |
130 |
137 |
|
|
|
|
|
|
|
|
| 100 |
109 |
114 |
118 |
124 |
129 |
136 |
|
|
|
|
|
|
|
| 98 |
105 |
109 |
113 |
117 |
123 |
128 |
134 |
|
|
|
|
|
|
| 96 |
101 |
104 |
108 |
112 |
116 |
121 |
126 |
132 |
|
|
|
|
|
| 94 |
97 |
100 |
103 |
106 |
110 |
114 |
119 |
124 |
129 |
135 |
|
|
|
| 92 |
94 |
96 |
99 |
101 |
105 |
108 |
112 |
116 |
121 |
126 |
131 |
|
|
| 90 |
91 |
93 |
95 |
97 |
100 |
103 |
106 |
109 |
113 |
117 |
122 |
127 |
132 |
| 88 |
88 |
89 |
91 |
93 |
95 |
98 |
100 |
103 |
106 |
110 |
113 |
117 |
121 |
| 86 |
85 |
87 |
88 |
89 |
91 |
93 |
95 |
97 |
100 |
102 |
105 |
108 |
112 |
| 84 |
83 |
84 |
85 |
86 |
88 |
89 |
90 |
92 |
94 |
96 |
98 |
100 |
103 |
| 82 |
81 |
82 |
83 |
84 |
84 |
85 |
86 |
88 |
89 |
90 |
91 |
93 |
95 |
| 80 |
80 |
80 |
81 |
81 |
82 |
82 |
83 |
84 |
84 |
85 |
86 |
86 |
87 |
|
| Category |
Heat Index |
Possible heat disorders for people in high risk groups |
| Extreme Danger |
130° or higher |
Heat stroke or sunstroke likely. |
| Danger |
105 – 129° |
Sunstroke, muscle cramps, and/or heat exhaustion likely. Heatstroke possible with prolonged exposure and/or physical activity. |
| Extreme Caution |
90 – 105° |
Sunstroke, muscle cramps, and/or heat exhaustion possible with prolonged exposure and/or physical activity. |
| Caution |
80 – 90° |
Fatigue possible with prolonged exposure and/or physical activity. |
|
