Washingtonians typically experience the hottest weather of the summer during July. Average high/low temperatures range from 88°/70° on July 1 to 88°/71° on July 31. In between, however, are DC’s warmest annual average high/low temperatures of 89°/71° from July 7 through July 22.
Thirteen of the last 20 July’s have been warmer than average in the Nation’s Capital. Four of DC’s 10 hottest July’s have occurred since 2010. DC’s hottest observed July temperature was 106° on July 20, 1930 and August 6, 1918.
It’s worth pointing out that weather records were measured downtown, and away from the moderating influences of the Potomac River, before National Airport opened in the early 1940s. DC weather records have been measured there ever since. DC’s coolest July temperature is 52° which has occurred more than once, most recently on July 4, 1933.
Since 1999, there have been a total of a 44 record
high and record high-low temperatures during the month of July in the Nation’s
Capital. A record “high-low” temperature
means a daily low temperature remained unusually warm. Over the same period of time, DC residents
have experienced only three record low-high temperatures, meaning three days
had significantly cooler than average high temperatures. DC hasn’t had a record low temperature during
the month of July since 1988. Part of
this can be attributed to the proximity of National Airport to the Potomac
River because it’s more difficult for areas on or near the water to heat up and
cool down that areas away from bodies of water.
The Nation’s Capital has also seen a more pronounced
urban heat island effect in recent decades.
That’s why temperatures away from National Airport are often much
different, especially in the winter. The
added pollution caused by increased population and development is also detrimental
to the environment.
Eleven of the last 20 July’s have been wetter than
average in Washington, D.C. The last two
July’s have had 9.15” and 9.73” of rain, respectively, in the Nation’s Capital.
That’s the only time DC has had more than 9” of rain in consecutive July’s in
the more than 140 years of record keeping.
That’s nearly triple DC’s July average of 3.73”.
The two very rainy July’s of 2017-2018 were memorable
as they occurred during very different stretches of weather in DC Metro Area. The period of August 2015 through March 2018
was a very dry period in the Nation’s Capital with an overall rainfall deficit
of 16.42”. On the other hand, April 2018
through December 2018 was an exceptionally rainy period with a rainfall surplus
of 27.8”, and 2018 became DC’s wettest on record.
NOAA expects a 33% chance for July 2019 to be a warmer
than average month in Washington, D.C., with an equal chance for above or below
average rainfall.
Washington,
D.C.’s Hottest July’s (Source: NOAA)
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)
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)
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