How unusual is triple-digit heat in the nation's capital?

 

DC's 7-day forecast (Source: The Weather Channel)

The nation’s capital is poised to experience one of its most intense heat waves in recent memory. High temperatures could reach or exceed 100° on four consecutive days starting this afternoon. Since triple-digit heat is so rare in the nation’s capital, having multiple consecutive 100-degree days would be an historic event. 

July is typically the hottest month of the year in the nation’s capital. As such, it isn’t surprising that triple-digit heat occurs most frequently in July. This century, Washington, D.C. has averaged one day of triple-digit July heat every other year, one such day every third August and one June day of triple-digit heat roughly every five to six years. This summer has already had one 100-degree day with a high of 100° on June 12. 

Triple-digit heat also tends to be feast or famine in the nation’s capital. For example, before the summer of 2024, that had six days of triple-digit heat, there hadn’t been any since 2016. The month with the highest overall number of 100-degree days in the nation’s capital remains July 2012 (7). However, the summer with the most 100-degree days remains 1930 with 11.

A heat wave is loosely defined as a minimum of three consecutive days that high temperatures reach at least 90-degrees. There have been multiple heat waves in the nation’s capital that didn’t have any triple-digit heat. The most notable such heat waves that occurred recently were a 12-day stretch in July 2019 and a 20-day stretch in 2020. However, while those heat waves were known primarily for their longevity, the upcoming heat wave will be known more for its intensity.

The typical summertime weather pattern in the United States is conducive for heat waves in the DMV (DC, Maryland and Virginia). That's when a semi-permanent area of high pressure sets up off the southeast coast of the United States. It's sometimes referred to as the "Bermuda High" since that's where they are often centered. The clockwise winds around this seasonal area of high pressure usher hot and humid air northward from the deep south into the Mid-Atlantic Region.

Tomorrow and Friday, July 2 and July 3, are setting up to be the hottest days in the DMV. That’s when temperatures are most likely to reach the triple-digit mark.

Longest streak of consecutive 100-degree days in Washington, D.C. (Source: NOAA)

Four Days

July 14 – 17, 2024
July 5 – 8, 2012
July 19 – 22, 1930

Three Days

August 13 – 15, 2016
July 8 – 10, 1993
July 15 – 17, 1988
August 3 – 5, 1930