What Can We Expect?

NOAA's temperature outlook for May

Although March and April were both drier than average in the Nation’s Capital, a major shift in the weather pattern has brought an extended period of unsettled weather to the Mid-Atlantic Region.  A total of 1.22 inches of rain has fallen in Washington, D.C. since April 27 which reduced the rainfall deficit that had grown to 3 inches just since March 1. 

Although there is no drought in the DC Metro Region, there has been some drier than average weather during the last few months.  Seven of the last nine months since last August have featured below average rainfall with a running deficit of 5.27” through April 30.  So, the rainfall that’s fallen the last few days has been quite beneficial for Washingtonians.

Like April, the month of May features a wide variety of weather in the Nation’s Capital.  The average high and low temperatures on May 1 are 71 and 52 degrees, respectively, and rise to 80 and 61 degrees on May 31.  Washington, D.C.’s hottest May daily temperature on record is 99 degrees, which occurred on May 31, 1991.  Its coldest May temperature on record is 33 degrees, which occurred on May 11, 1936.  Area residents should also be pleased to know that average highs will be at least 70 degrees in the Nation’s Capital from now through October 12. 

May is also the wettest month of the year in Washington, D.C. with 3.99” of rain on average.  However, five of the last six Mays have featured below average rainfall in the Nation’s Capital according to the National Weather Service.  Yesterday we received 0.48” of rain at National Airport, whereas that much rain didn’t occur until May 16 in 2015.  Concurrently, there is also a stretch of six consecutive warmer than average Mays in Washington, D.C.  Area residents may recall that May 2015 narrowly surpassed May 1991 as being the warmest on record.

A key factor that enhances May’s rainfall chances is the higher frequency of showers and thunderstorms that typically occur during the spring.  For example, a powerful EF5 tornado developed in Moore, Oklahoma as part of an outbreak of more than 30 tornadoes on May 20, 2013; and on May 8, 2008 when 10 tornadoes occurred from North Carolina to Maryland.

May has also featured cooler than average weather.  An example is May 2003, which was more than four degrees cooler than average in the Nation’s Capital and also significantly wetter than average.  NOAA’s temperature outlook for this May is for a 40% chance it will be warmer than average, but only a 50-50 chance for above average monthly precipitation.