The burning question

The burning question

Dear Ace: Is it the heat or the humidity?—Elke Summer

Elke: We’ve all got that cousin in Arizona who gleefully tells us that though it gets up to 120 degrees during the dog days of summer, it’s a dry heat. As if feeling like you’re in a sauna is going to stop your flip-flops from bonding to the sidewalk. But your cousin’s probably right. Being outside in Central Virginia in the middle of the summer can be an absolutely miserable experience. So is it the humidity?


Just 92 degrees at 100 percent humidity—far from unheard of in Virginia—is as bad as being out in 132 degree weather with no humidity

Yep. The heat index is a number that gets relevant when the humidity starts climbing. In a place like Arizona, the heat index isn’t really fiddled with because humidity remains constantly low. But in Virginia, where heat waves can drive heat and humidity up to unbearable levels, heat index is right on every climatologist’s mind come summertime. The heat index is derived from a complex equation that combines humidity and air temperature to provide an idea of how hot it feels. Even this is a rather inexact way of describing it, however, considering the way a certain temperature feels with Virginia’s humidity levels is what we’re used to around these parts. Perhaps a better way of explaining the whole heat index thing is that it can be used as a guide to the effects of a certain heat-humidity combo. According to National Weather Service data, for example, 110 degrees at 40 percent humidity is as dangerous as 136 degrees with no humidity. Just 92 degrees at 100 percent humidity—far from unheard of in Virginia—is as bad as being out in 132 degree weather with no humidity.

So what does all this mean? Is it that terrible to be outside when it feels like it’s pushing 140 degrees? Yes again. John Stenger, a research coordinator with UVA’s state climatology office, told The Daily Progress a few years ago, "When the dew points get high, it becomes very difficult for the body to cool itself via perspiration. This is why very high temperatures combined with high dew points can become life-threatening under certain circumstances." And according to NWS data, heat-related deaths in the U.S. between 1992 and 2001 where humidity was the major culprit numbered 2,190, more than twice the number of deaths from hurricanes and flooding combined from the same period. So, Elke, it’s the humidity. Big time. After all this scary heat index mess, Ace is thinking he might need to find a cooler place this summer. Does Harris Teeter rent out their walk-in freezers?

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