How common is 90-degree May heat in DC?

 

A warm May evening in Washington, D.C.

Washingtonians can expect to see the first 90-degree temperature of the year on or around May 18 on average. The nation’s capital averages 36 days per year with high temperatures of at least 90° with the majority coming in June, July, and August. The nation’s capital has averaged between one and two 90-degree May days over the last 30 years.

Interestingly, Washingtonians experienced 90-degree May heat in three of the last four years. That doesn’t predict how hot the subsequent summer will be. For example, May 2016 was cooler than average in the nation’s capital. No 90-degree heat occurred in 2016 until June 11. However, the summer of 2016 went on to become the third hottest on record (at the time) in the nation’s capital. 

DC’s earliest 90-degree day on record was on March 22, 1907 (90°). The latest first 90-degree temperature in the nation’s capital occurred on July 12, 1979 (93°). Both of those summers were significantly cooler than average. This illustrates that no correlation exists between when the first 90-degree temperatures occur and whether or not a summer is warmer than average.

Washingtonians sometimes experience 90-degree heat before May begins. The nation’s capital averages one 90-degree April day every three to four years. September also averages between three and four 90-degree days in the nation’s capital.

A “heat wave” is loosely defined as three or more consecutive days in the 90s. The nation’s capital has experienced three of those in May over the last 30 years, with the most recent being in 2019. DC had only one 90-degree day last May, but that was a record-tying high of 91° on May 2. No triple-digit heat has occurred in the nation’s capital in May, but highs reach 95° roughly once every five years with the most recent on May 31, 2022 (96°).

It hasn’t been 90° or hotter in Washington, D.C. since August 29, 2024 (93°). No 90-degree is expected either in the nation’s capital during the upcoming week.