Heat advisory noon to 8 p.m. | Code orange air quality alert: Unhealthy for sensitive groups *

6:05 p.m. – Dulles ties record, while other locations end up well short

High temperatures Monday ranged from 91 to 94 in Washington, Dulles, and Baltimore. Dulles, which hit 94, tied the record high for the date set in 2007. Baltimore also hit 94, but fell three degrees short of its record. Washington, which only reached 91, was six degrees shy of its record.

But humidity more than made up for the under-performing heat. The combination of heat and humidity made it feel like 100 to 105 as predicted.

4:15 p.m. – Heat index values exceed 100, but temperatures mostly fall short of records

Heat index values (what it feels like factoring in temperature and humidity) have eclipsed 100 this afternoon throughout the region, generally peaking between 100 and 105. However, clouds and the high moisture levels have held back actual air temperatures to around 90 to 94 degrees – below record levels. Dulles Airport, which has at least risen to 93 degrees, may still match or exceed its record of 94 from 2007.

Original post from 11:14 a.m.

Areas under heat advisory June 18. (National Weather Service)

The combination of heat and humidity could make it feel as hot as 105 degrees Monday afternoon, which prompted the National Weather Service to issue a heat advisory for the Washington region within about a county of the Interstate 95 corridor.

Air temperatures are forecast to reach 93 to 98 degrees, meaning record high temperatures in Washington, Dulles and Baltimore of 97 (from 1944), 94 (from 2007), and 97 (from 1957) are all potentially within reach.

But humidity levels will make it feel five to 10 degrees hotter. Dew points, an indicator of humidity, are in the very muggy low 70s.

The sultry air was already palpable by midmorning Monday. On social media, Capital Weather Gang readers expressed their dismay.

It’s “like living under a steamed blanket,” tweeted Cara Thuringer.

“It’s already at that point outside, where you walk outside, and begin dripping in sweat in about a minute, even if you’re not actually doing anything,” reader Bryan Grimaldi posted to Facebook.

Forecast heat index values at 5 p.m. from NAM model.

The National Weather Service urged people to take precautions in the hottest weather of the year so far. “The heat and humidity may cause heat stress during outdoor exertion or extended exposure,” it said. It advised the following:

  • Reschedule strenuous activity to early morning or evening
  • Wear light weight and loose fitting clothing
  • Drink plenty of water

It also recommended that outdoor workers take frequent rest breaks in air-conditioned environments.

In addition to the possibility of record highs Monday afternoon, temperatures will be slow to cool overnight Monday meaning low temperatures Tuesday morning may also rank highest on record. The existing record high minimum temperatures in Washington, Dulles and Baltimore on Tuesday are 75 (from 2011), 71 (from 2014)  and 74 (from 1905).

Although Tuesday afternoon temperatures are forecast to reach the 90s for a second straight day, they’ll probably fall short of the records in Washington, Dulles and Baltimore of 99, 98 and 99, all from 1994. Clouds and late-day storms are likely to break the heat before temperatures can climb that high.

The Weather Service issues a heat advisory in the Washington region when the heat index (or feels-like temperature) is forecast to reach at least 105 degrees. Over the past decade or so, it has issued five or six heat advisories per summer on average. Monday’s heat advisory is the first of 2018.

When the heat index is forecast to reach at least 110 degrees, the Weather Service issues an excessive-heat warning, which is a more serious alert. Although Monday’s weather was notable for being the hottest weather of the season so far, the region can and probably will experience hotter conditions in July and/or August.