D.C.’s Warm and Wet Start to May

Glen Echo Park, Glen Echo, Maryland

D.C.’s weather during the first 20 days of May 2018 can be broken into two very different halves.  Ten days were warmer than average in the Nation’s Capital over the first 11 days of May.  In addition to the very warm start of the month, Washingtonians didn’t see any measurable rainfall until May 12.  During May’s very warm and dry start, some area residents remembered that May 2015 was D.C.’s warmest on record and was also much drier than average.

However, comparisons to May 2015 were premature since Washington, D.C. had measurable rainfall on eight consecutive days (May 12 – May 19).  D.C.’s record for most consecutive days with measurable rainfall is 15 that occurred relatively recently (April 27, 2016 - May 11, 2016).  D.C.'s second and third longest streaks of consecutive days with measurable rainfall are 11 and nine days, respectively, that have each occurred more than once dating back to the 1870s.  National Weather Service data indicates that D.C.’s eight-day streak of measurable rainfall earlier this month would tie for the fourth longest on record.  

What makes this month’s stretch of rainy weather stand out is the amount of rain that occurred. Washingtonians experienced seven consecutive days with at least 0.4” that broke the old record of five such days.  To add to that, D.C. tied its existing record of four consecutive days with 0.75”/+ of rain (May 16 – May 19).  More significantly, the three previous times the four consecutive days occurred were all in either September or October.  That marks another weather first that occurred last week in the Nation’s Capital.  

May 2018 has certainly lived up to its billing as the wettest month of the year on average in the Nation’s Capital.  With 6.14” of rain through May 21, this month has been D.C.’s wettest month since last July.  However, Washington, D.C. would need a rainfall total of at least 6.97” by May 31 for this month to rank among the ten wettest May’s on record.  

Not only has this month been significantly wetter than average in the Nation’s Capital, but D.C.’s average monthly temperature through May 20 has been 6.7° above average.  That’s rather unusual because wetter than average months are often cooler than average, like May 2016 and May 2017 both were in D.C.  Nine of D.C.’s ten wettest May’s on record finished with below average monthly temperatures according to the National Weather Service.  For example, May 2003 had a record 20 days with measurable rainfall that made it D.C.’s eighth wettest and was also the coolest May in the Nation’s Capital since 1967.

NOAA expects warmer than average temperatures to continue in the Mid-Atlantic Region with several additional chances for rain through the end of May.  This combination could enable this month to finish among both D.C.’s warmest and wettest May’s on record.