\"It's no the heat, it's the humidity\". That's a partly valid phrase you may have heard in the summer, however it's actually both. The heat index, also known as the apparent temperature, is what the temperature feels prefer to the human body once relative humidity is an unified with the wait temperature. This has essential considerations because that the human body's comfort. Once the body gets as well hot, it begins to perspire or sweat come cool itself off. If the perspiration is not able to evaporate, the body cannot manage its temperature. Evaporation is a cooling process. As soon as perspiration is evaporated off the body, it efficiently reduces the body's temperature. As soon as the atmospheric moisture content (i.e. Relative humidity) is high, the price of evaporation indigenous the body decreases. In various other words, the human body feeling warmer in humid conditions. The contrary is true when the loved one humidity decreases due to the fact that the price of perspiration increases. The body in reality feels cooler in arid conditions. There is straight relationship in between the air temperature and relative humidity and the heat index, an interpretation as the air temperature and also relative humidity increase (decrease), the heat index rises (decreases).

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Figure 1. Warm index chart.
In stimulate to recognize the warmth index using the graph above, you need to recognize the wait temperature and the family member humidity. Because that example, if the waiting temperature is 100°F and the loved one humidity is 55%, the warm index will certainly be 124°F. When the loved one humidity is low, the apparent temperature deserve to actually be lower than the air temperature. For example, if the air temperature is 100°F and also the relative humidity is 15%, the warmth index is 96°F (use this calculator). In the Panhandles, we commonly see warm temperatures throughout the summer, however the low relative humidity values make it rather unusual to watch dangerous heat index worths (i.e. 103°F or greater). A complete heat table of contents chart for a larger range of temperatures and also relative humidity values have the right to be uncovered at this link.

It surprises many civilization to find out that the warmth index worths in the chart above are because that shady locations. If you are exposed to direct sunlight, the heat index value deserve to be boosted by up to 15°F. As displayed in the table below, heat indices meeting or exceeding 103°F can lead come dangerous heat disorders with an extensive exposure and/or physical task in the heat.

Classification
Heat IndexEffect ~ above the body
Caution80°F - 90°FFatigue feasible with an extensive exposure and/or physical activity
Extreme Caution90°F - 103°FHeat stroke, heat cramps, or warmth exhaustion possible with prolonged exposure and/or physics activity
Danger103°F - 124°FHeat cramps or heat fatigue likely, and heat stroke possible with an extensive exposure and/or physical activity
Extreme Danger125°F or higherHeat stroke very likely

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If you're yes, really mathematically inclined, over there is an equation that provides a very close approximation come the warmth index. However, this equation was obtained using a many regression analysis, and also therefore, it has an error of±1.3°F.Heat table of contents = -42.379 + 2.04901523T + 10.14333127R - 0.22475541TR - 6.83783 x 10-3T2 - 5.481717 x 10-2R2 + 1.22874 x 10-3T2R + 8.5282 x 10-4TR2 - 1.99 x 10-6T2R2T - wait temperature (F)R - relative humidity (percentage)