The First Half of August: A Closer Look

 

The first half of August has featured some memorable weather in the Nation’s Capital.  It got off to a blissful start with cooler than average temperatures on six of the first seven days.  Relative humidity was also comfortably low at more fall-like levels with dewpoint temperatures often in the 50s across the D.C. Metro Area.  That allowed for the full assortment of outdoor activities free of the more typical early-August uncomfortable heat and humidity.

Rainfall was also scarce during the first week of August.  But, there was a rather pronounced shift in DC’s weather pattern during the second 10 days of the month.  Between August 11 and August 20, Washingtonians saw a total of 6.75” of rain – more than double D.C.’s August average of 3.25”.  Two of those days featured rainfall of more than 2”.  Through August 20, a total of 7.99” of rain has occurred in the Nation’s Capital.  

Consequently, with measurable rainfall on 12 of the first 20 days of August, temperatures have largely been at or just below average.  However, the reason monthly temperatures are within 0.2° of average is because of a seven-day heat wave from August 8 – 14.  Since then, there has been only one day with highs in the 90s.  Temperatures next week are poised to shift again as NOAA’s Climate Prediction Center expects warmer than average temperatures for the D.C. Metro Area during the next six to 10 days (August 27 – 31).

There are a few parallels between D.C.’s weather last August and so far this month.  August 2020 finished as a wetter than average month with 8.73” of rain, making it D.C.’s thirteenth wettest.  With the final third of August 2021 remaining there’s a good chance Washingtonians could eclipse last August’s rainfall total.  

In August 2020, the combination of cloudy, rainy days and the frequent rainfall produced a high level of ground level moisture that all combined to keep high temperatures cooler than they otherwise would have been.  Consequently, August 2020 had a total of only seven days with highs in the 90s.  There have already been nine such days this month, with several more 90° days on tap during the upcoming week.

Although the early part of next week is looking sunny and hot with highs in the low 90s, there will be several more chances of showers and thunderstorms.  The prospect of additional rainfall coupled with several more days in the 90s should help this month finish wetter and warmer than average.  D.C.’s last cooler than average August occurred in 2017, while the last drier than average August in the Nation’s Capital was in 2019.