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Capital Weather Gang

Intense, extended heat wave to last through Monday

By
July 19, 2017 at 1:54 p.m. EDT
A steamy sunset in Washington, July 18. ( <a href="https://www.flickr.com/photos/clif_burns/35881808541/in/pool-capitalweather/">Clif Burns via Flickr</a> )

The temperature in Washington has soared to at least 90 degrees in Washington for three straight days, and the heat will only grow more intense heading into the weekend.

This heat wave is destined to be the hottest and longest-lasting of the summer (so far).

“Historically the latter part of July is the hottest period of the year in the Mid-Atlantic, and this weekend will definitely fit that descriptor,” the National Weather Service office serving the Washington region said Wednesday morning.

Friday and Saturday are likely to be the hottest days, when highs reach the upper 90s to around 100. Factoring in the humidity, it will feel like 105 to 110 degrees.

By the heat wave’s final day next Monday, the region will have posted eight straight days with highs of at least 90 — passing the year’s two previous longest streaks of six days.

Just how hot?

Depending on your preference for computer models, highs Thursday through Sunday will range between 98 and 101 or 96 and 98 in Washington. The GFS model is most aggressive with the heat, predicting some triple-digit highs, while the European model caps temperatures several degrees lower:

GFS model forecast highs Thursday to Monday

  • Thursday: 98
  • Friday: 99
  • Saturday: 100
  • Sunday: 101
  • Monday: 90

European model forecast highs Thursday to Monday

  • Thursday: 94
  • Friday: 97
  • Saturday: 97
  • Sunday: 97
  • Monday: 93

Nighttime temperatures are also predicted to be unusually warm, with lows hovering near 80, or perhaps even a couple of degrees higher Friday through Sunday.

Note that these temperatures are for the environment around downtown Washington. Cooler suburban areas, especially north and west of the city, will tend to be several degrees cooler — with highs mostly in the mid-90s and overnight lows in the 70s.

Punishing humidity

Factoring in the humidity, it will feel several degrees hotter than the air temperature each day.

Afternoon heat index values should at least reach 100 every day through Monday, and may peak in the range of 105 to 110 degrees Friday and Saturday.

Dew point temperatures, an indicator of humidity, should generally hover between 70 and 75 degrees — in the muggy range. Sunday and Monday, it would not be surprising to even see some dew points above 75, entering the sultry range.

Records?

As this heat wave coincides with our hottest time of year historically, some of the records will be tough to match. For example, Thursday’s record high of 106, set in 1930, matches the highest temperature ever recorded in Washington. We won’t threaten that one. In fact, none of the record highs through Monday seem to be in peril. These are the existing record highs and the years they were set:

  • July 20: 106 from 1930
  • July 21: 104 from 1926
  • July 22: 103 from 1926
  • July 23: 102 from 2011
  • July 24: 101 from 2010

Heat readiness tips

As long as this 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.