I'm just back from a run in the Arb, which is green and glowing with humidity. The air temp is about 80 degrees F, but the 80% relative humidity pushes the heat index up to about 85 degrees F. This is just about the hottest day of 2008, so I wondered whether we've had a 100-degree swing of temperatures yet this year.
Looking back at my training log, I see that it was rather cool on New Years Day. I skied just after noon, when the wind chills were down around -20 degrees F. Tack that onto today's current temperature and we get a nice 100-degree swing - at least perceptually: heat index and wind chill are both imaginary "feels-like" measures. Which is useful when ignoring them and heading outside.