August is Heating Up

High temperatures in the Nation’s Capital today will flirt with the 90° mark.  Several more days of 90° heat are on tap this week and Washingtonians are poised for one more heat wave before the end of August.  A “heat wave” is defined as a minimum of three consecutive days of 90° heat. 

As DC residents know, July 2020 was DC’s third warmest on record with 28 days of 90° heat.  But this month has been a different story.  Although it was 0.8° warmer than average through August 22, it has also been cooler than recent Augusts.  Four of the last five August’s have been warmer than average in the Nation’s Capital, with 2017 being the exception. 

So far this month there have been only four days of 90° heat, well below the total of 16 such days last year.  With several more days in the 90s during the upcoming week, the Nation’s Capital should finish between 2013’s total of six August 90° days and 2017’s nine such days.

Dating back to the early 1990s, the Nation’s Capital averages approximately 11 days of 90° August heat.  Of those 11 days, roughly three days feature high temperatures between 95° and 99°.  Washingtonians have seen triple-digit heat roughly every three to four years during the month of August.  The last time 100° heat occurred was in August 2016. 

While August is DC’s second warmest month of the year behind July, partially due to the gradually decreasing amounts of daylight, August can be warmer than July on occasion.  In fact, from 2000 – 2009, the month of August was warmer than July seven times in Washington, D.C.  However, since 2010, August has been warmer than July only once (2018).  The summer of 2016 was a very hot one in the Nation’s Capital, with July and August both finishing with the same monthly average temperature of 82.7° (combining daily high and low temperatures). 

There have been several notable late August heat waves in the Nation’s Capital in three of the last four years.  Some might wonder if this month’s above average rainfall has contributed to the lower number of 90° days.  While cloudy and/or rainy days can reduce high temperatures, it is possible to have both a very warm and wet month. 

Such was the case in August 2018, which finished 2.9° warmer than average with monthly rainfall more than 2” above average.  This month has been even wetter with over 6” of rain (more than double DC’s August rainfall average of 2.93”).  It has also had more cooler than average days (six) compared to all of August 2018 (four).  The moral of the story is that while August 2020 should finish close to 1° of average while being significantly wetter than average, it won’t be one of DC’s warmest or wettest August’s.