What Should Washingtonians Expect as April Turns to May ?

April 2019 finished as DC’s second warmest on record with an average temperature of 62.4° -- significantly above the monthly average of 56.8°.  The Nation’s Capital has now had warmer than average Aprils in 11 of the last 12, including the two warmest on record in the last three years.  Last month was also drier than average in Washington, D.C. with only 2.24” of rain (0.82” below average).  It was DC’s first drier than average month since last October.

May is the third and final month of meteorological spring.  Average temperatures rise considerably from today’s high/low of 71°/52° to 80°/61° on May 31.  DC’s hottest May temperature on record was 99° on May 31, 1991.  Meanwhile, DC’s coldest May temperature was 33° on May 11, 1906.  Four of DC’s 10 warmest May’s have occurred in the last 15 years, including DC’s warmest May on record in 2015.  While weather records in Washington, D.C. date back to 1871, they have been kept at National Airport since 1942.  Prior to that weather observations were made downtown.

Over the last 20 years, there have been 11 warmer than average May’s.  Given the warmer weather in May, there is typically an uptick in the frequency of thunderstorms and severe weather.  Maryland averages one May tornado, while Virginia averages two.  Last month had an unusually high amount of severe weather in the Mid-Atlantic Region, with confirmed tornadoes in the DC-Baltimore Metro Area on both April 19 and April 26.

The month of May is also DC’s wettest of the year on average with 3.99”.  There have also been six May’s in the last 20 years that were both wetter and cooler than average in the Nation’s Capital.  Four of DC’s 10 wettest May’s have occurred just since 2003, including last May that was DC’s sixth wettest on record.  

The first few months of 2019 have produced a unique trend of measurable rainfall on 11 of the first 17 Friday’s of the year.  Moreover, there have been only three completely dry Friday’s during the first four months of 2019.  NOAA’s outlook for May calls a significant chance of above average temperatures this month, with an equal chance for above or below normal rainfall in the Mid-Atlantic Region.