Because muggy is a term used to express a feeling of moisture in the air, many people think the relative humidity will dictate how muggy the air feels outside. However, the relative humidity in the winter can be 90% which is not considered to be muggy. On an 89 degree summer day, a relative humidity of 90% would be a muggy day indeed! To understand this difference, you must consider the dew point temperature.
The higher the dew point temperature, the more muggy the air will feel leading to increased chances of summer heat illnesses such as heat stroke (or sun sickness), and heat exhaustion. While not an official scale, the Answers@NOAA website lists a dew point scale (below) which can help you determine how muggy the air outside feels. Forget what the local weather forecast says about the relative humidity, think instead of the dew point temperature - The higher the dew point temperature, the hotter (or "muggier") it feels.
Muggy Weather Scale - Dew Point Temperature in Degrees Fahrenheit
- Less than 50....Not Muggy
- 50 - 59...Slightly muggy
- 60 - 69...Moderately muggy
- 70 - 79...Very muggy
- Greater than 79...Unbearable!