Hottest Month of the Year ?

July is the second month of “meteorological” summer, which runs from June through August.  It is the hottest month of the year on average in the Nation’s Capital, ahead August.  July is also the third wettest month of the year with a total of 3.73”.

Average high/low temperatures in Washington, D.C. are 88°/70° on July 1 and 88°/71° on July 31.  However, D.C.’s warmest daily average temperatures of the year are 89°/71° from July 7 through July 22.  The hottest July temperature on record is 106° on July 20, 1930.  That’s tied with August 6, 1918 for D.C.’s hottest overall temperature.  July’s coolest observed temperature in Washington, D.C. is 49° and has occurred three times, most recently on July 29, 1986.  Eight of the last 10 July’s have been warmer than average according to NOAA.

This trend of July being hotter than average frequently over the last decade has coincided with some dramatic, record-setting July heat waves.  A “heat wave” is defined as a minimum of three consecutive days with temperatures of 90°/+.  Washington, D.C. has had heat waves of at least 11 days in four of the last 10 July’s.  Washingtonians sweat through a 16-day heat wave from July 18 to August 2, 2011, that saw four days of triple-digit heat.  That was followed by an 11-day heat wave from June 28 to July 8, 2012.  A total of five days of triple-digit heat occurred in that 11-day span.

Rainfall in July is variable as thunderstorms occur frequently during the summer months.  However, the location that thunderstorms form can be unpredictable.  For example, National Airport can see heavy rain on some days, while little or no rain falls in the nearby suburbs of Bethesda or Bowie.  Since 1998, there have been 10 wetter than average and 10 drier than average July’s in Washington, D.C.  Infrequently, the D.C. Metro Area can feel the impacts of decaying tropical systems in July.  In 1996, the remnants of Hurricane Bertha brought appreciable rainfall to Washington, D.C. after it made landfall in North Carolina.

While July is often the hottest month of the year overall, the longest heat wave of the summer doesn’t always occur in July.  For example, while Washingtonians experienced a 14-day heat wave in June 1994, July 1994 finished with an average monthly temperature (combining daily high/low temperatures) more than 2° warmer than June.  NOAA expects this July to be a warmer than average month in the D.C. Metro Area with near average precipitation.