Heat Index Chart The NWS has devised the "HEAT INDEX" (HI), sometimes called the "apparent temperature." The HI is the temperature the body feels when the heat and humidity are combined. The table below is the Heat Index Chart. (Note: This chart is based upon shady, light wind conditions. Exposure to full sunshine can increase HI values by up to 15 F.) Air Temperature (Degrees F) 70 75 80 85 90 95 100 105 110 115 120 Relative Humidity Heat Index 0% 64 69 73 78 83 87 91 95 99 103 107 10% 65 70 75 80 85 90 95 100 105 111 116 20% 66 72 77 82 87 93 99 105 112 120 130 30% 67 73 78 84 90 96 104 113 123 135 148 40% 68 74 79 86 93 101 110 123 137 151 50% 69 75 81 88 96 107 120 135 150 60% 70 76 82 90 100 114 132 149 70% 70 77 85 93 106 124 144 80% 71 78 86 97 113 136 157 90% 71 79 88 102 122 150 170 100% 72 80 91 108 133 166 Heat Index Readings and Potential Heat Related Disorders: 85 to 94 degrees F - Caution: physical activity may cause fatigue 95 to 105 degrees F - Extreme Caution: possible heat cramps and/or heat exhaustion with prolonged exposure Above 105 degrees F - Danger: possible heat stroke with prolonged exposure; heat exhaustion and heat cramps likely