Understanding and Calculating the 'Feels Like' Temperature

The "feels like" temperature, also known as the apparent temperature, represents how the human body perceives the ambient temperature, considering factors like humidity and wind speed. This metric provides a more accurate sense of comfort than the actual air temperature alone.

What Is the 'Feels Like' Temperature?

The "feels like" temperature adjusts the actual air temperature based on environmental conditions that affect human comfort:

• Humidity: In hot conditions, high humidity impairs the body's ability to cool itself through sweat evaporation, making it feel hotter.

• Wind Speed: In cold conditions, wind increases heat loss from the body by moving the warm air layer near the skin, making it feel colder.

Calculating the 'Feels Like' Temperature

The calculation method depends on the prevailing weather conditions:

1. Cold Conditions (Wind Chill):

When temperatures are below 50°F (10°C) and wind speeds exceed 3 mph, the wind chill index is used. The formula is:

Wind Chill (°F) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Where:

• T is the air temperature in °F.

• V is the wind speed in mph.

This formula accounts for the increased heat loss from the body due to wind. (climate.umt.edu)

2. Warm Conditions (Heat Index):

When temperatures are above 80°F (27°C), the heat index is used to determine the "feels like" temperature. The formula is:

HI = -42.379 + 2.04901523*T + 10.14333127*RH - 0.22475541*T*RH - 0.00683783*T^2 - 0.05481717*RH^2 + 0.00122874*T^2*RH + 0.00085282*T*RH^2 - 0.00000199*T^2*RH^2

Where:

• T is the air temperature in °F.

• RH is the relative humidity as a percentage.

This formula combines temperature and humidity to estimate the apparent temperature, reflecting how hot it feels. (climate.umt.edu)

Example Calculation

Consider a scenario where the air temperature is 90°F (32°C) with a relative humidity of 70%. Using the heat index formula:

HI = -42.379 + 2.04901523*90 + 10.14333127*70 - 0.22475541*90*70 - 0.00683783*90^2 - 0.05481717*70^2 + 0.00122874*90^2*70 + 0.00085282*90*70^2 - 0.00000199*90^2*70^2

Calculating this yields a heat index of approximately 105°F (41°C), indicating that it feels much hotter than the actual air temperature due to the high humidity.

Limitations and Considerations

While the "feels like" temperature provides a useful estimate of human comfort, it has limitations:

• Direct Sunlight: Exposure to direct sunlight can make conditions feel warmer than the calculated "feels like" temperature.

• Clothing and Activity Level: The type of clothing worn and the level of physical activity can significantly affect thermal comfort.

• Individual Variations: Personal factors, such as acclimatization and health status, can influence how temperature is perceived.

Understanding the "feels like" temperature is essential for making informed decisions about outdoor activities, dressing appropriately, and ensuring safety in varying weather conditions.

For a visual demonstration and further explanation of calculating the heat index, you might find this video helpful:

How to Calculate Heat Index or Feels Like Temperature