Beware: More triple-digit heat coming

 

Dangerous heat will impact many eastern cities (Source: NOAA)

While June is DC’s third hottest month of the year, triple-digit heat isn’t as common as it is in July or August. Today will be the first 90-degree day of what will likely become a record-setting heat wave in the nation’s capital. A “heat wave” is loosely defined as three or more consecutive days with high temperatures of at least 90°. 

By the time this heat wave is over, the nation’s capital could have experienced as many as two or three days of triple-digit heat. Longtime Washingtonians know the combination of high temperatures and relative humidity are what makes the summer months particularly uncomfortable.

While summers in DC are often hot and humid, 100-degree air temperatures are relatively rare.  Before last summer, the nation’s capital hadn’t seen any triple-digit heat since August 15, 2016.  Prior to June 22, 2024, there hadn’t been any triple-digit June heat in Washington, D.C. since 2012.

Having one day of triple-digit heat this week would set some impressive weather benchmarks in the nation’s capital. These statistics are from the National Weather Service. Weather records in Washington, D.C. date back to 1871.

 

1. 100-degree June heat in DC has occurred only twice in consecutive June’s:

1933, 1934
2010, 2011, 2012

2. DC has experienced 100-degree June heat more than once only twice: 1959, 1874
 

3. DC has experienced 100-degree June heat on consecutive days only once:

June 29 – June 30, 1959

 
4. Longest stretch without triple-digit June heat (years):

37: 1874 – 1911
19: 1969 – 1988
18: 1934 – 1952
14: 1911 – 1925
13: 1997 – 2010
12: 2012 – 2024

Triple-digit June heat in Washington, D.C.

100° - June 5, 1925
102° - June 9, 1874
100° - June 9, 1933
102° - June 9, 2011
100° - June 10, 1964
101° - June 11, 1911
101° - June 15, 1994
101° - June 22, 1988
100° - June 22, 2024
100° - June 24, 2010
100° - June 25, 1997
101° - June 26, 1952
100° - June 26, 1954
100° - June 28, 1969
101° - June 29, 1874
101° - June 29, 1934
100° - June 29, 1959
104° - June 29, 2012
100° - June 30, 1959

A closer look at dangerous June heat

 

A summer's day in the nation's capital

The hottest weather of the year will soon get underway in the nation’s capital. High temperatures early next week will reach the mid to upper 90s across the DMV (DC, Maryland and Virginia). That will be similar to last year’s record-setting June heat wave that brought the nation’s capital its first triple-digit heat in nearly eight years. It’s worth taking a closer look at the terms “heat wave” and “extreme heat.” 

A ”heat wave” is loosely defined as three or more consecutive days when high temperatures reach the 90s. Extreme heat, meanwhile, can be one or two very hot days without meeting the heat wave criteria. For example, a heat wave occurred in the nation’s capital from June 7 – June 12, 2011. However, there were only two extremely hot days during that six-day stretch with highs of 99° and 102°, respectively, on June 8 and 9. A record high of 99° also occurred on June 17, 2022, but that was the only 90-degree day of the week.

June 1959 finished on an exceptionally hot note in the nation’s capital with highs of 100° on both June 29 and June 30. Making this extreme heat stand out is how it remains the only time triple-digit heat has occurred on consecutive June days in the nation’s capital. Triple-digit heat qualifies as extreme heat whether or not it occurs during a heat wave.

A similar example occurred in June 1925 when the nation’s capital experienced an eight-day heat wave from June 1 – June 8. A shorter period of extreme heat occurred within that heat wave when DC experienced five consecutive record highs from June 2 – June 6. DC’s record high of 100° on June 5, 1925, remains the earliest in the calendar year triple-digit heat has ever occurred. Helping illustrate how unusual such extreme early June heat is that all these record highs still stand a century later. 

The June 1925 heat wave is also remarkable since the nation’s capital was much less developed then. There is much more urbanization and automobile traffic now and that enhances the urban heat island effect. Overnight low temperatures remain warmer which makes heat waves more extreme. For example, DC’s average low temperature during the five-day period of June 2 – June 6, 1925, was 70.8°. By comparison, the average low temperature during the five-day period of June 22 – June 26, 2024 was 75°.

Next week’s heat wave will feature potential record-challenging heat in the DMV. Consequently, it will be important to drink plenty of water and take lots of breaks in air conditioning to prevent heat-related illness. 

Weather Quiz

 

A June view of the Washington Monument

True or False.

The nation’s capital has never experienced more than one day of triple-digit heat in June.