July Comes to a Warm and Wet Conclusion

July will finish warmer than average for a fifth consecutive year in the Nation’s Capital and for the eighth time in the last 10 years.  That’s in large part to DC’s longest heat wave in nearly three years.  It was also a wetter than average month for a third consecutive year.

The 12-day heat wave from July 11 – 22 was the longest Washingtonians experienced since August 2016.  Although no record highs were set, DC had its hottest temperature of 99° (July 21) since August 15, 2016.  There have been 21 days of 90° heat this month in Washington, D.C.  That’s helped July 2019 rank among the warmest on record in the Nation’s Capital.  DC’s average monthly temperature (combining daily high and low temperatures) through July 30 is 82.1°.

The weather pattern was favorable for a lot of warmer than average weather coupled with many very humid days.  That was due in large part to the semi-permanent summer feature known as the “Bermuda High.”  This phenomenon refers to a sprawling area of high pressure that typically sets up during the summer months off the East Coast of the United States near the island of Bermuda.  The southerly/southwesterly winds that blow around the area of high pressure help pump warm and humid air northward from the Gulf Coast toward the Mid-Atlantic Region.  

A series of fronts have also impacted the DC Metro Area during July, bringing frequent showers and thunderstorms to the Nation’s Capital.  Since July 1, a total of 6.48” of rain has fallen in Washington, D.C., well above July’s average of 3.73”. DC’s wettest day this month occurred on July 8 with a daily record 3.44” at National Airport.  However, only 1.05” of rain fell at Dulles Airport on July 8; and a below average total of 2.71” has fallen there this month.  That helps illustrate how localized heavy rain associated with summertime showers and thunderstorms can be.  

As wet as this month has been in the Nation’s Capital, the last two July’s were wetter.  More than 9” of rain occurred in Washington, D.C. in both July 2017 and July 2018.  That was the first time on record that 9” or more rain occurred in consecutive July’s in the Nation’s Capital.  The potential exists for showers and thunderstorms this afternoon as well as the next several days.  August 2019 has the potential to pick up where July left off, with frequent shower and thunderstorm chances.

Warmest July’s in Washington, D.C. by Average Temperature (Combining Daily High/Lows)

1.  84.5° (2011)
2.  84.0° (2012)
3.  83.1° (2010, 1993)
5.  83.0° (1999)
6.  82.7° (2016)
7.  82.6° (1987)
8.  82.3° (1980)
9.  82.1° (1955)
10.  81.9° (1988)

---

Most 90° Days in July in Washington, D.C.

1.  25 – 2011
2.  24 – 1993, 1987
4.  23 – 2016, 1988
6.  22 – 2012
7.  21 – 2019
8.  20 – 2017, 2010