Dewpoint vs Humidity

The dew point is often considered a better indicator of comfort than relative humidity for several reasons:

Direct Measure of Moisture Content

• Dew Point: The dew point directly measures the amount of moisture in the air. It is the temperature at which air becomes saturated and water vapor begins to condense. The higher the dew point, the more moisture in the air.
• Relative Humidity: Relative humidity, on the other hand, is a percentage that represents the current amount of moisture in the air relative to the maximum amount the air can hold at that temperature. It changes with temperature, so it can be misleading.

Consistency and Sensation

• Dew Point: Provides a more consistent measure of how humid it feels because it is not dependent on temperature. For instance, a dew point of 60°F (15.6°C) will generally feel humid regardless of whether the air temperature is 70°F (21°C) or 90°F (32°C).
• Relative Humidity: Can be high at cooler temperatures but may not feel uncomfortable. For example, 70% humidity at 60°F (15.6°C) feels much different than 70% humidity at 90°F (32°C).

Impact on Human Comfort

• Dew Point: Higher dew points (above 60°F or 15.6°C) are often associated with discomfort because the air feels muggy or sticky, which can hinder the body’s ability to cool itself through sweating.
• Relative Humidity: High relative humidity at low temperatures might not be noticeable in terms of comfort, whereas high relative humidity at high temperatures can feel oppressive.

Predictability

• Dew Point: Allows for better predictability of comfort levels. Dew points over 70°F (21°C) are usually considered very uncomfortable, while dew points under 50°F (10°C) are typically comfortable.
• Relative Humidity: Less predictable for comfort as it varies greatly with temperature. For instance, 50% relative humidity can feel different in winter versus summer due to temperature differences.

Summary

In essence, the dew point is a more straightforward measure that better reflects human perception of humidity and comfort. It consistently indicates the actual amount of moisture in the air and how oppressive or comfortable the air will feel, independent of temperature changes. This makes it a more reliable metric for assessing and predicting comfort levels in various weather conditions.