Weather Word of the Week: Dew point

It’s a hot summer day and you hear someone say, “The relative humidity is 80%!” They’re probably correct, but relative humidity is just not a good way to measure how muggy the air “feels” to our bodies.

Warmer air can hold more water vapor than cooler air, so 80% percent humidity “feels” much different when the air temperature is 90 degrees Fahrenheit, as opposed to, say, 50. Instead, the dew point temperature is a much better measurement of how much water vapor is hanging in the air.

Dew point is the temperature that an air parcel must be cooled to at constant pressure and constant water vapor content in order for saturation to occur. So, when the dew point and air temperature are the same, the humidity is 100%. Usually, that only happens during rain, snow, or fog.

The dew point is always at or below the air temperature; it’s impossible for it to be higher. And the greater the difference between the dew point and air temperature, the drier the air will feel.

Dew points below 50 are considered dry, and dew points between 50 and 60 are generally ideal. Most people start to feel the humidity when dew points are between 60 and 70, and when the dew points get above 70, that’s when it feels like Florida outside, or as we like to say, the air you can wear.

When you combine high dew points with air temps in the 80s, 90s, or even 100s, that’s when you can get heat index values that are dangerous to human health.

Dew points of 80 degrees are rare in our region, but the highest dew point ever recorded in Toledo was 81 degrees! That happened on June 18 of 2018. Lastly, you want to know the highest dew point ever recorded planet Earth? 95 degrees! That was in Dhahran, Saudi Arabia in July of 2003.

So just remember, when you’re trying to determine how muggy the air is, don’t look at the humidity percentage; instead, refer to the current dew point.

Latest Local News | First Alert Weather | Crime | National | 13abc Originals