Lesson 7 - Understanding Wind and Humidity Factors - Page 2

It's not the heat, it's the humidity

An old cliché, but a true one: hot, humid weather definitely makes people feel more uncomfortable than hot, dry weather. Humidity is moisture, and high humidity levels slow the human body's evaporation of sweat--nature's method of cooling--because damp air can't absorb moisture as much or as quickly as dry air.

Often, high humidity is merely an annoyance; it makes people feel sticky or touches off a week of bad hair days. But sometimes high humidity can be life-threatening--unaware of its dangerous effects, fitness fans attempting to exercise outside on humid days have been known to literally drop from heat stroke; children and the elderly can unknowingly overexert themselves and become seriously ill.

Lingo Links

When words branch off from one root...

 Humid:  from the Latin humidus; wet or damp

The meaning of other words become clearer...

humidify, humidistat, humidor

To warn people of the risks of exercising in hot, humid weather, the "Apparent Temperature Table" serves as a guideline to apparent temperature--that is, how hot various temperature-humidity combinations will feel to humans--and also indicates levels of danger associated with a given apparent temperature.

The row and column format of the chart makes it easy to read. For example, to find the apparent temperature on a day when the recorded temperature reaches 95° and the relative humidity is measured at 50 percent, a person simply finds 95° in the temperature column on the left side, and follows that row to the right until it intersects the 50 percent humidity column, where the apparent temperature reads 107°. Not surprisingly, the shades on the chart that suggest levels of danger in various combinations indicate that an apparent temperature of 107° falls into the "danger" area where outdoor exercise is not a wise idea.

But unlikely though it is that any reasonably intelligent person would decide to run a 25 mile marathon in 107° temperatures, it should be remembered that the Apparent Temperature Table can not account for individual differences in exercise programs, age, or general health. What might be an acceptable apparent temperature to a well-toned twenty year old jogger could prove fatal to a weekend athlete with diabetes. For that reason, the chart offers words of warning, not medical advice!

Relative Humidity (percent)
  0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
140 125                                        
135 120 128                                      
130 117 122 131                                    
125 11 115 123 131 141                                
120 107 111 118 123 130 139 148                            
115 103 107 111 115 120 127 135 142 150                        
110 99 102 105 108 112 117 123 130 137 143 150                    
105 95 97 100 102 105 109 113 118 123 129 135 142 149                
100 91 93 95 97 99 101 104 107 110 115 120 126 132 138 144            
95 87 88 90 91 93 94 96 98 101 104 107 110 114 119 124 130 136        
90 83 84 85 86 87 88 90 91 93 95 96 98 100 102 108 109 113 117 122    
85 78 79 80 81 82 83 84 85 86 87 88 89 90 91 93 95 97 99 102 105 106
80 73 74 75 76 77 77 78 79 79 80 81 81 82 83 85 86 86 87 89 89 91
75 69 69 70 71 72 72 73 73 74 74 75 75 76 76 77 77 78 78 79 79 80
70 64 64 65 65 66 66 67 67 68 68 69 69 70 70 70 71 71 71 71 71 72
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