Today's word is: dewpoint

Ugh. Record power consumption levels in Ontario. "The agency that monitors electricity use in Ontario has issued a power warning and is asking consumers to cut back on usage as demand soars. Terry Young, of the Independent Electricity System Operator, recommends consumers keep air conditioners in the 26 degree range, keep blinds and curtains closed and avoid using major appliances between 8 a.m. and 8 p.m." Roger.

melted_snowball mentioned dewpoint in his "gawds it's hot" post, and I still didn't understand it, so I did a little reading, so I might as well share my new-found knowledge. And that is: dewpoint is a good measure to use when you're talking about awful humidity. wikipedia was all about the formulae, but they pointed to a page by accuweather which spelled things out nicely (if you're willing to use Fahrenheit).

The dewpoint temperature is the saturation point of the air, or the temperature to which the air has to be cooled in order to get condensation. It's an absolute measure of humidity, versus relative humidity, which goes down as the temperature goes up (and the humidity stays constant). A dewpoint above 20 degrees C (70F or so) will feel quite humid, and above 26 C (80F) is sauna-like. It's currently 23 here, and I think it was close to 27 or 28 last night when I walked the dog at 10pm (very close to the temperature; which meant the humidity was about 100%; which explained why I felt like I was in an invisible fog bank. Ugh.)

Comfortable dewpoints are from 10C - 15C (50F - 60F). In that range, sweat will easily evaporate and remove heat from your body. As moisture in the air increases, sweating is less effective since the air's approaching saturated, and your sweat doesn't evaporate.

Humidex and its American cousin "Real Feel Temperature" (hey accuweather, isn't there a less dippy name for that?) are based on dewpoint.