Summer’s Midway Point

Nationals Park, Washington, D.C.

Now that we are at the unofficial halfway point of the 2017 summer season, we can reflect upon how this summer compares to average so far.  Meteorological summer runs from June 1 through August 31.  True to form, the month of June and the first half of July have featured plenty of above average temperatures.

June 2017 finished 2.1° warmer than average in the Nation’s Capital and included 8 days of at least 90°.  Last month was also exceptionally dry in Washington, D.C. with only 1.13” of rain at National Airport.  That made for the third driest June on record in the Nation’s Capital.  The dry month of June that Washingtonians experienced has been part of a larger weather pattern with 19 of the last 23 months being drier than average since August 2015.  Had May not been appreciably wetter than average, DC residents would have endured a Top 15 driest first half of the year.

July has gotten off to a hotter and wetter than average start in Washington, D.C. with 12 days of 90° heat through July 16.  There have been a total of 23 days of 90° so far this year.  By comparison, the Nation’s Capital didn’t experience day 23 day of at least 90° until July 26 last year.  There has already been 3” of rain so far this month in the Nation’s Capital and that’s just under the total of 3.13” that occurred in all of last July.

The relative humidity has made it feel much worse.  Wind direction plays a critical role in both temperature and relative humidity in the Nation’s Capital.  Winds on the hottest days in Washington, D.C. tend to be westerly, meaning they blow from west to east, while the more humid days have southerly winds.  

There was a good example of just how big a difference that a change in wind direction can make in temperatures and relative humidity this past Friday.  On July 14, the 1 PM temperature at National Airport was 92° with a dewpoint temperature of 78° and a south wind of 10 mph.   However, at 2 PM, the winds shifted to W at 16 mph with gusts to 23 mph.  The change in wind direction helped temperatures jump to 97° and the dewpoint drop to 71°.