“It’s not the heat, it’s the humidity.” You’ve likely heard this saying during summer, and there’s truth to it. While air temperature is what a thermometer reads, the heat index provides a more complete picture of how hot it actually feels to our bodies. This is why understanding “what’s the temperature” goes beyond just the number on a screen, especially when humidity is high.
The heat index, also known as the apparent temperature, combines air temperature and relative humidity to reflect the human body’s perception of warmth. Our bodies regulate temperature through perspiration, or sweating. As sweat evaporates, it cools us down. However, humidity significantly impacts this cooling process.
In high humidity, the air is already saturated with moisture, hindering sweat evaporation. This reduced evaporation means our bodies can’t cool down as efficiently, leading to a sensation of feeling hotter than the actual air temperature. Conversely, in dry conditions with low relative humidity, sweat evaporates more readily, making us feel cooler than the thermometer reading. Therefore, to truly understand “Whats The Temperature” feels like, we must consider both the air temperature and the humidity.
Heat Index Chart
Figure 1. Heat index chart demonstrating how apparent temperature rises with increases in both air temperature and relative humidity.
The heat index chart (Figure 1) is a valuable tool to determine this apparent temperature. To use it, locate the air temperature on one axis and the relative humidity on the other. The point where they intersect reveals the heat index. For example, at an air temperature of 100°F and 55% relative humidity, the heat index is a sweltering 124°F. Interestingly, when humidity is low, the apparent temperature can be lower than the actual air temperature. At 100°F with only 15% relative humidity, the heat index drops to a more manageable 96°F. You can also use online heat index calculators for precise values.
It’s crucial to remember that these heat index values are calculated for shady conditions. Direct sunlight can increase the heat index by up to 15°F, making it feel significantly hotter. Furthermore, high heat index values pose serious health risks.
The National Weather Service categorizes heat index levels and their associated dangers:
| Classification | Heat Index | Effect on the body |
|---|---|---|
| Caution | 80°F – 90°F | Fatigue possible with prolonged exposure and/or physical activity. |
| Extreme Caution | 90°F – 103°F | Heat stroke, heat cramps, or heat exhaustion possible with prolonged exposure and/or activity. |
| Danger | 103°F – 124°F | Heat cramps or heat exhaustion likely, heat stroke possible with prolonged exposure/activity. |
| Extreme Danger | 125°F or higher | Heat stroke highly likely. |
As you can see, heat indices of 103°F or higher are considered dangerous, potentially leading to heatstroke and other heat-related illnesses, especially with prolonged exposure or strenuous activity. When considering “whats the temperature”, always factor in humidity and consult the heat index to understand the real risk and take necessary precautions to stay safe in hot weather.
