Summer-like Heat on Tap

Heat Index  (Source: NOAA)

Summer officially arrives in the northern Hemisphere during the month of June.  Although DC’s highest average temperatures don’t occur until July, some of the hottest weather on record in the Nation’s Capital has occurred in June.  No correlation exists between a hotter or cooler than average month of June in Washington, D.C., and what the rest of the summer will be like. 

Since 1993, Washingtonians have averaged more than 7 June days of 90° heat, nearly 2 days of 95° heat with 100° heat in June roughly every five years.  June has been hotter than average in Washington, D.C. in nine of the last ten years, but seven of the previous ten Junes, dating back to 1997, were cooler than average.  That helps illustrate that above or below average monthly temperatures tend to be cyclical.  For example, from 2010 through 2012, June averaged 13 days at/above 90° while from 1997 through 2000 Washingtonians saw an average of only 6 days at/+ 90°.

June 1994 ranks as the second hottest on record in the Nation’s Capital with 17 days of at least 90°, including a stretch of 14 consecutive 90° days.  However, that was the hottest stretch of the summer and included a record high temperature of 101° on June 15.  That would be the last 100° in Washington, D.C. for more than three years.  Washingtonians didn’t experience their first 90° heat until June 11 last year, with only five 90° through June 30, 2016.  However, from July 1 through September 30, 2016, the Nation’s Capital sweat through 53 days at/above 90° including 4 days of 100° heat.

The hottest June temperature on record in Washington, D.C. is 104° (that occurred on June 29, 2012).  However, that’s narrowly below DC’s overall record high temperature of 106° that occurred once each in 1918 and 1930.  More recently, June has seen bouts of extreme heat such as in 2010, which surpassed 1994 as being DC’s warmest June on record.  While there was only one more June day of 90° heat (18) than occurred in June 1994, what made the difference were the warmer overnight low temperatures.  That essentially means overnight low temperatures didn’t cool off as much in June 2010, as they did 16 years earlier.

Washingtonians are poised to experience their first heat wave (3 or more consecutive days at/above 90°) starting on Sunday.  Some record high temperatures will likely be approached as well but no 100° is expected at this point.  However, the combination of temperatures in the 90s and higher relatively humidity will make the heat index temperature meet or exceed the century mark.

                                                        Record High Temperatures

June 12

DCA: 95° (2002)
IAD: 96° (1986)
BWI: 96° (1986)

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June 13

DCA: 96° (1954)
IAD: 94° (1994)
BWI: 97° (1956)