What Makes May 2020 So Unusual ?

Although May 2020 had a warm and dry final few days, it has been a cool and dry month overall.  Through yesterday, DC’s average temperature this month was more than 2° cooler than average.  It will also finish as a drier than average month, making this May DC’s first cooler and drier than average one since 2006.

DC’s warmest temperature this month was 87° on May 29, while the coolest temperature was 37° on May 9.  This will be DC’s first May since 2016 without any 90° heat.  That’s unusual since DC’s average first 90° temperature of the year occurs on or around May 18.  By comparison, DC’s warmest May in 2015 saw seven days of 90° heat.  The Nation’s Capital also had its first record low-high temperature during the month of May since 2003 when it was only 52° on May 9.  

Having a cooler than average May without any 90° temperatures isn’t a good predictor of what the upcoming summer will be like, however.  Such was the case in 2016 when DC residents didn’t see the first 90° of the year until June 11.  Yet, the summer of 2016 finished as DC’s third warmest on record overall.

This month has also been drier than average.  Some may find that surprising considering the many rainy days.  Rain occurred on 18 days this month, but only produced a total of 2.49”, which is 1.5” below DC’s May average.  More than a third of that rainfall total occurred on May 3, when Washingtonians had 0.93”.  Following a cool and rainy April, the Nation’s Capital is in good shape rainfall wise with a rain surplus for the year of 1.27”.  

May 2020 will finish as a fairly unique weather month in the Nation’s Capital without any 90° heat.  That’s combined with the fact it’s been DC’s first cooler and drier than average May in more than a decade.  While NOAA is expecting June to be warmer than average with near average precipitation in the DC Metro Area, its three-month forecast calls for wetter and warmer than average conditions.