DC’s hottest month gets underway

A warm summer's evening in Washington, D.C.

July is D.C.’s hottest month of the year based on the average daily high/low temperatures kept by NOAA. The hottest days are from July 11 - 27, when average high/low temperatures are 90°/73°. NOAA’s climate averages are based on 30 years of data and are updated every decade. NOAA updated its averages in 2021 to reflect the period from 1991-2020, and replaced the previous data set from 1981-2010.

Since the 2010s were a much warmer decade than the 1980s, D.C.’s average daily high temperature increased from 89° to 90° for most of the month. That should not surprise longtime Washingtonians as seven of D.C.’s 10 hottest July’s have occurred since 2010. Consequently, D.C.’s average July temperature for the 30-year period from 1981-2010 was 79.8° but rose to 81.0° when updated to reflect the newer time period.

D.C.’s hottest July temperature on record is 106° on July 20, 1930. More recently, D.C.’s second hottest temperature of 105° was on July 7, 2012. D.C.’s coolest July temperature of 52° has occurred three times, most recently on July 4, 1933. Weather records in the nation’s capital date back to 1871.

Last July was D.C.’s fourth warmest on record and featured four consecutive days of triple-digit heat. That was only the third time such a torrid stretch occurred in the nation’s capital. D.C.’s two previous instances of four consecutive days of triple-digit heat also occurred in July (1930 and 2012).

July’s new monthly rainfall average of 4.33” also makes it D.C.’s wettest month of the year. That represents a significant increase over the old average of 3.73”. Two of D.C.’s 10 wettest July’s at National Airport occurred within the last decade (2017 and 2018). NOAA’s Climate Prediction Center is expecting this July to be a warmer and wetter than average month in the D.C. Metro Area, continuing the recent trend.

Warmest July’s in Washington, D.C. by average temperature (Source: NOAA)

1. 84.5° (2011)
2. 84.0° (2012)
3. 83.9° (2020)
4. 83.7° (2024)
5. 83.1° (2010, 1993)
6. 83.0° (1999)
7. 82.7° (2016)
8. 82.6° (1987)
9. 82.3° (1980)
10. 82.1° (2019, 1955)