When Does DC typically see its First 90° Temperature ?

NOAA's Temperature Outlook, May 24 - 30

Washingtonians can expect to see the first 90° temperature of the year on or around May 18 in an average year.  Appropriately, temperatures will approach the 90° plateau for the first time in 2019 this Sunday, May 19.  The Nation’s Capital averages 36 days per year with high temperatures of at least 90° with the majority coming during the summer.  The Nation’s Capital has averaged between 1 and 2 90° May days since 1993.

Interestingly, last May got off to a very warm start with 90° on three of the first four days of the month.  By comparison, roughly 7.5 months since the last time temperatures reached 90° in Washington, D.C. on October 4, 2018.  DC’s warmest May on record occurred recently in 2015 and included seven 90° days.  May 2015 was also the last drier than average May in the Nation’s Capital. 

Meanwhile, May 2016 was cooler and wetter than average.  In fact, in 2016 DC didn’t observe its first 90° until June 11.  However, the summer of 2016 went on to become the third hottest on record in the Nation’s Capital with an average temperature of 80.5°.  This helps illustrate that no correlation exists between when the first 90° temperatures occur and whether or not a summer is warmer than average.  DC’s earliest 90° on record was on March 22, 1907 (90°), while the latest first 90° temperature occurred on July 12, 1979.  Both of those summers were ultimately cooler than average.

Last May was a little unusual in the Nation’s Capital where it was the third warmest and sixth wettest on record.  The first heat wave of 2018 (three or more consecutive days of 90°/+) occurred on May 2-4 and was DC’s earliest first heat wave since 2002.  No measurable rainfall occurred in the Nation’s Capital last May until May 12.  A wetter than average streak then occurred with measurable rainfall on eight consecutive days through May 19.

Meanwhile, this May has featured the opposite weather pattern in the DC Metro Region with measurable rainfall on seven of the first 13 days of the month.  Despite no 90° heat, May 2019 has been 2.7° warmer than average through May 16.  That can largely be attributed to warmer than average low temperatures in the Nation’s Capital with eight such days in the 60s – more typical of June than the first half of May. 

NOAA expects warmer than average temperatures with below average rainfall during the next 1 to 2 weeks so it will start to feel more like summer as Memorial Day approaches.  That will give the Nation’s Capital a chance to dry out.

NOAA's Precipitation Outlook, May 22 - 26