Dewpoint

"It's not the heat, it's the humidity," we used to say. And, to an extent, we were right. But a more accurate measurement of the uncomfortableness of the summer weather is the dewpoint. I should point out that I'm not a professional meteorologist, but I am interested in weather. I think we all understand heat. Humidity is expressed as a percentage, and it's the percentage of moisture in the air comparative to what the air can hold. The hotter it is, the more moisture the air can hold, so the hotter is it, the lower the humidity can be and still seem sticky. (For about every 10 degrees Celcius, or 18 degrees Farenheit, the temperature goes up, the amount of moisture the air can hold doubles. So at 80 degrees the air can hold twice as much moisture as at 60 degrees, which is why a higher humidity at 60 doesn't feel as uncomfortable.) The dewpoint, or dewpoint temperature, as I understand it, is the critical temperature at which condensation (in the form of dew or fog) appears, or the relative humidity hits 100%. That is, if you cool the air without changing the moisture content, you'd reach a temperature (the dewpoint) at which the air can no longer contain the moisture it holds. So dewpoint more accurately measures how "moist" the air feels.

Dewpoints in the 60s generally feel kind of sticky. Dewpoints in the 70s (and today it's about 75 here in Fairmont, with a temperature of about 86) are described as "tropical." Yesterday the dewpoint was over 80, which has been described as "unbearable."

Pretty good for a non-science guy, eh?