The Washington PostDemocracy Dies in Darkness

Heat index soars to 106 degrees as Washington confronts summer’s hottest day

Belle the Chihuahua, right, jealously waits her turn as the big dog, Rocky, gets the first crack at the water dish. Both used the water hose provided by the park. The Wheaton Dog Park is popular even on very warm days because it has lots of shade and a water hose and several community dog bowls. (Michael S. Williamson/The Washington Post)
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(This story, originally published at 12:45 p.m., was updated at 3:10 p.m. and 5:30 p.m.)

* Heat advisory through 8 p.m. for heat index values up to 105 *

Washingtonians described Thursday’s air as like a “turkish bath,” “thin onion broth,” “dog breath” and “moist death.”

Indeed, the combination of heat and humidity was brutal — the hottest of the summer so far, and temperature climbed to near record levels.

The temperature in Washington (as measured at Reagan National Airport) soared to 97 degrees Thursday afternoon, but felt as hot as 106 degrees factoring in the humidity.

Cloud cover stopped temperatures from soaring even higher, so Washington missed the record high for the date of 100 degrees, set in 1954. Computer models, such as the high resolution NAM model had forecast highs up to around 99 degrees.

Dulles Airport, which rose to 94 degrees, also fell three degrees shy of its record of 97 degrees, set in 1986 and 1966.

Similarly, Baltimore’s high temperature of 95 degrees was four off its record of 99 degrees, set in 1966, 1954 and 1880.

From your brain to your skin pores, this is what goes into your body keeping you cool when the heat turns up. (Video: Claritza Jimenez/The Washington Post)

Of course, the humidity was as big a story as the heat. Dew point temperatures, an indicator of the humidity level, hovered in the low to mid-70s — which is in the muggy or “gross” range, bordering on the oppressive.

Taking the heat and humidity together, the heat index — a measure of how hot it feels — climbed into triple digits by midday and registered 106 degrees at 3 p.m. and 5 p.m. in Washington.

Triple digit heat index values were widespread along the East Coast on Thursday, from New York City into the Carolinas.

The thick humid air has prevented nighttime temperatures from cooling down appreciably. As a result, Washington was likely to set a record for its warmest low (minimum) temperature Thursday. The low temperature as of early evening was just 79. Assuming there’s no cooling thunderstorm before midnight, the previous record warm low of 78, set in 1993, 1992 and 1981, will be broken.

On Wednesday, Washington tied its warmest low temperature for the date of 77, set in 2011.

While Thursday marked the heat wave’s hottest day, it’s not over. On Friday, the temperature may sprint up to near 95, with a heat index near 100, before showers and thunderstorms cool us down in the afternoon and evening.

Dry weather as well as relief from the heat and humidity arrive this weekend.

Keeping cool during a Washington heat wave

WASHINGTON, DC - JULY 11: Jakai Tunstall, 6, passes through a cascade of water as children play in the fountains at The Yards Park as a heat wave passes through the DC area on Tuesday, July 11, 2017, in Washington, DC. Today's heat was kept in check by overcast clouds for much of the day, but the temperatures are expected to rise as we move into the week. (photo by Jahi Chikwendiu/The Washington Post)

As long as this excessive heat lasts, remember the following tips to stay safe and cool:

  • Check on vulnerable individuals, especially older adults who live alone and/or anyone without access to air conditioning.
  • Stay hydrated.
  • Take air-conditioned breaks if working or exercising outside and, if possible, shift strenuous activity from the afternoon hours to the evening or early morning.
  • Never leave a young child or pet alone in a hot car.
  • Protect your pets by keeping them indoors and off hot pavement, and providing water.