(This story, originally published at 11:24 a.m. Wednesday morning, was updated at 3:15 p.m. Wednesday afternoon to add the heat advisory issued for Thursday, and to slightly lower predicted high temperatures Wednesday.)

* Heat advisory noon to 8 p.m. Thursday for air temperatures in the mid-to-upper 90s and heat index values up to 105 degrees *

The summer’s hottest days so far have arrived and have a chance to threaten long-standing records across the region.

Temperatures today are likely to soar into the mid-90s in Washington and could touch the century mark on Thursday. If the temperature reaches 100 Thursday, it would tie the record established in 1954.

HRRR model forecast highs on Wednesday.

Factor in the humidity, and it will feel about five degrees hotter each day. As the heat index could potentially hit 105 degrees Thursday, the National Weather Service issued a heat advisory for the region.

Note that temperatures in cooler locations, especially north and west of the Beltway, may be five degrees or so lower than downtown.

Heat index forecast at 2 p.m. Thursday from GFS model.

On Wednesday, the D.C. government activated its heat emergency plan because temperatures were expected to reach at least 95 degrees, which opens cooling centers throughout the city. It will inevitably do the same on Thursday.

In addition to the predicted hot afternoons, the next two nights are expected to be unusually warm with lows only in the upper 70s to near 80 in urban areas, near the highest minimum temperatures on record. The lack of night time cooling can cause a dangerous buildup in heat stress for the homeless and those without air conditioning.

During this hot weather, it is important to check on vulnerable individuals, particularly older adults living alone. Stay hydrated and take air-conditioned breaks if working or exercising outside. Never leave a young child or pet alone in a hot car. Also protect your pets by keeping them indoors and off hot pavement, and providing water.

During a heat wave the body has to work harder to maintain a normal body temperature. Here are five facts to keep in mind when dealing with intense heat. (Claritza Jimenez/The Washington Post)

The worst of the heat exits the region Friday, setting up a nice, less humid midsummer weekend.

Records

For reference, here are the record high maximum and minimum temperatures at our three local observing sites Wednesday and Thursday; those in bold have the best chance to be challenged:

Washington

  • Wednesday: High max: 99 (set in 1908) | High min: 77 (set in 2011)
  • Thursday: High max: 100 (set in 1954) | High min: 78 (set in 1993, 1992 and 1981)

Dulles

  • Wednesday: High max: 97 (set in 1986) | High min: 72 (set in 2006)
  • Thursday: High max: 97 (set in 1986 and 1966) | High min: 74 (set in 2016)

Baltimore

  • Wednesday: High max: 97 (set in 1908) | High min: 77 (set in 1936 and 1935)
  • Thursday: High max: 99 (1966, 1954 and 1880) | High min: 77 (set in 1880)