Major Shift in DC’s Weather Pattern

 

The weather in the Nation’s Capital during the first half of May 2021 has been both cooler and drier than average.  May is normally one of the nicest weather months of the year in D.C. with average highs in the 70s.

During the first half of May, Washingtonians have experienced predominantly cooler than average weather, including every day since May 6.  That’s resulted in an average monthly temperature (combining daily high and low temperatures) for May 1 – May 17 of 2.7° below average.  Many D.C. Area residents may recall that last May finished more than 2° cooler than average also.

However, there will be a major shift in the weather pattern this week to more summer-like weather as the jet stream changes course.  High temperatures today will flirt with 80° before soaring into the 80s tomorrow.  Highs will reach the low 90s later in the week in parts of the D.C. Metro Area.  That would be right on schedule as the average first 90° day of the year in Washington, D.C. occurs on or around May 18. 

While there wasn’t any 90° heat in the Nation’s Capital last May for only the second time in a decade, Washingtonians have averaged between one and two 90° days in May dating back to the early 1990s.  Not surprisingly given the shift in the weather pattern, NOAA’s Climate Prediction Center expects the next two weeks to be warmer than average in the Mid-Atlantic Region.  That means there’s a good chance DC’s average monthly temperature for May 2021 will finish very close to average despite the cool start to the month.

This month has also had a gotten off to a drier than average start with only 0.69” of rain as of May 17.  The Nation’s Capital is running a rainfall deficit of more than 2” since March 1.  Some may find that hard to believe since there have been a fair number of days with rain.  None of the rain has been particularly heavy, though.  My colleagues and I on the WUSA9 Weather Team don’t expect rain before the weekend at the earliest.

The good news about the warm temperatures arriving by the end of the week is that it won’t be particularly humid.  The warmer temperatures will actually feel pleasant absent the higher relative humidity levels so common across the D.C. Metro Area in July and August.