Much has been made of Death Valley’s simmering 129-degree reading Sunday, matching the hottest temperature ever measured in June in the U.S. But a common refrain I’ve heard from many Washingtonians is: “But it was a dry heat.” And there’s some truth to that.
Dew points, the temperatures below which water droplets begin to condense and excellent indicators of humidity, were in the arid 30s in Death Valley when the mercury shot up to that 129-degree milestone. Using the National Weather Service’s nifty calculator, that temperature and dew point combination produced a heat index of only around 116 or 117 degrees. In short, the very low humidity (and low dew points) in Death Valley made the air feel cooler than the actual temperature.
Of course, the situation is reverse in Washington, D.C. during heat waves. The humidity makes the air feel hotter. Let’s turn back the clock two years to July 22, 2011, the height of D.C.’s “sweat ceiling” heat wave. On that day, Washington, D.C. had a temperature/dew point combination of 102/78, leading to a heat index of 121. Yes, that’s several degrees hotter than Death Valley Sunday.
D.C.’s hottest known heat index (dating back to 1977) occurred July 16, 1980, when a temperature/dew point combination of 103/78, produced a heat index of 122.
How does that 122 heat index compare with Death Valley’s hottest weather ever recorded?
On July 10, 1913, Death Valley allegedly (some meteorologists dispute the reading) hit 134, the highest reading ever measured anywhere in the world. But the dry air surely made it feel cooler than that. Unfortunately, dew points weren’t observed in 1913. But unless they were higher than the low 40s (extremely doubtful), the heat index did not exceed 122.
Do D.C.’s heat indices, as high or higher than Death Valley, mean it should be considered the hottest location in the world? Not quite. Others places have experienced even more oppressive combinations of heat and humidity. Doyle Rice of USA Today describes an obscene heat index of 155-160 reached in Saudi Arabia:
….according to the weather record book Extreme Weather by Christopher Burt, Dharhan, Saudi Arabia, on the Persian Gulf, had a heat index of around 155-160 degrees on July 8, 2003, which is the highest of which Burt is aware. He reports that the air temperature was 108 degrees at that time, with an incredible dew point of 95 degrees.
Next time D.C. has a heat index of 110, I’ll remind everyone of this….