Beware July heat

 

NOAA's July temperature outlook (Source: NOAA)

June 2024 finished as DC's second warmest (behind only 2010) and fourth driest (1.15") on record. We had the first triple-digit heat since August 15, 2016, along with D.C.'s first triple-digit June heat since 2012.

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 D.C.’s 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.

During the earlier 30-year period, D.C.’s hottest average daily high temperature was 89° for most of July. However, 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 six 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. That’s tied with a date in August for D.C.’s hottest overall temperature. 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.

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 (Combining Daily High/Lows: NOAA)

1. 84.5° (2011)
2. 84.0° (2012)
3. 83.9° (2020)
4. 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)