DC’s hottest time of the year?

 

The White House, Washington, D.C.

Washingtonians often experience some of the hottest weather of the summer during mid-to-late July. That’s when average daily high temperatures are at the highest of the year at 90°. The weather pattern is often such that hazy, hot and humid conditions dominate local weather headlines.

More triple-digit heat has occurred in July than any other month in the nation’s capital. All but three July days have seen triple-digit heat since official weather records began in 1871. There are three days in mid-July that 100-degree heat has occurred five times in the nation’s capital: July 16, July 17, and July 21. 

There’s been no triple-digit heat so far this summer. That’s in contrast to last summer that featured six days of triple-digit heat and finished as DC’s third hottest summer. Last summer was also DC’s first summer since 2011 that 100-degree heat occurred in three consecutive months (June, July and August). 

As hot as last summer was, it also helped illustrate how rare 100-degree days are in the nation’s capital. Before last summer no triple-digit heat had occurred in Washington, D.C. since August 15, 2016. The nation’s capital averages only one to two days of triple-digit heat every four to five years.

High temperatures in the mid to upper 90s are more common than triple-digit air temperatures are in the nation’s capital. Washingtonians saw highs of 99° during the summers of 2019, 2020 and 2022 during the nearly eight-year streak without triple-digit heat. It has already been as hot as 99° so far this summer as well.

Weather observations for the nation’s capital are made at National Airport. A southerly wind at National Airport blows off the cooler waters of the Potomac River. That tends to keep the air temperature a few degrees cooler during summer than downtown areas away from the river. That doesn’t mean, however, it’s any less humid or uncomfortable. Some Washingtonians lament how humid it is in the nation’s capital during the summer, as opposed to the southwestern United States where it’s hotter, but a “dry heat.”

The major takeaway is that while triple-digit heat is relatively rare in the nation’s capital, the most likely time for it to occur is in mid-to-late July given historical weather data. But triple-digit heat isn’t necessary for dangerously hot conditions in the DMV (D.C., Maryland and Virginia) given how oppressive the summer months often are. Drinking extra water, doing outdoor activities early in the day when its cooler, and applying suntan lotion are all good summer safety tips.