Memorable June Heat Waves in the Nation’s Capital

 

 

 

Summer officially gets underway in June, but DC’s hottest weather doesn’t typically arrive until July and August.  Nevertheless, Washingtonians have had some memorable heat waves during the month of June.  Five of DC’s 10 warmest Junes have occurred just since 2010.

2020:  Although last June finished with a near average total of nine 90° days, the majority of those days occurred during a five-day heat wave from June 26 – June 30.  By comparison, this year’s first heat wave was from June 5 – June 7.  A “heat wave” is a minimum of three consecutive days high temperatures reach at least 90°.

2011:  DC’s fourth warmest June was noteworthy for several reasons.  The longest heat wave of the month was a six-day event from June 7 – 12.  It included two record highs: 99° on June 8 and 102° on June 9.  The June 9 temperature of 102° tied the existing record for the date.

2010:  This was the warmest June on record in the Nation’s Capital with 18 days of 90° heat, including an 11-day heat wave from June 19 – 29.  Six of those 18 days had high temperatures of 95°/+.  DC residents had a record high of 100° on June 24.  That was also DC’s first instance of triple-digit June heat since 1997.  Although more than a decade had passed since the last time Washingtonians experienced triple-digit heat in June, June 2010 was the first of three consecutive June’s with 100° heat.

1997: This was an unusual June since it got off to a very cool start.  The June 3 high temperature of 58° set a new record for DC’s coolest high temperature for the date.  There was a major shift in the weather pattern during the second half of the month, with a nine-day heat wave from June 20 – 28.  The hottest day was June 25 that featured a record high of 100°.  Despite the impressive heat during the final third of the month, June 1997 was still a cooler than average month.

1994: For nearly two decades, June 1994 held the distinction of DC’s hottest on record.  It also featured the longest heat wave of the summer with a 14-day heat wave from June 13 – 26.  The hottest day was June 15 with a record high temperature of 101°.  A total of five record highs were set during the month, including three consecutive records from June 14 – 16 that still stand today.  No June has had more than one day of 100° heat in the Nation’s Capital.

High Impact Early Season Tropical Storms and Hurricanes

 

Flooding from Tropical Storm Allison, June 2001  (Source: NOAA)

Hurricane season in the Atlantic Ocean Basin runs from June 1 - November 30.  June and November are typically the quietest months of the season when atmospheric and environmental conditions are the least favorable for development.  That’s not to say there haven’t been a few high impact tropical storms and hurricanes during the month of June.

Debby (2012):  Tropical Storm Debby was an example of how a tropical system doesn’t have to be intense to have significant impacts.  That’s because both tropical storms and minimal hurricanes have the potential to bring significant amounts of rain, along with coastal flooding and beach erosion.  Such was the case with Debby across much of central and northern Florida, where isolated rainfall totals of more than 20” were observed.  The heavy rain attributed to Debby and its remnants helped make June 2012 the wettest on record in Tampa.

Allison (2001):  While it was only a tropical storm at peak intensity when it made landfall in Texas, Allison achieved a dubious honor.  It was the first of only two Atlantic tropical storms to have had its name retired by the World Meteorological Organization.  Tropical storm and hurricane names are retired for being very damaging and/or deadly (e.g. Katrina, Andrew, Michael).  What made Allison unique wasn’t its intensity, but its longevity.  After making landfall in Texas, its remnants lingered for days and caused devastating flooding.

Agnes (1972):  Agnes became a minimal hurricane over the eastern Gulf of Mexico on June 18, but isn’t remembered for that.  As a weaker tropical storm, Agnes menaced much of the Mid-Atlantic and northeastern United States where its remnants caused widespread flooding.  Multiple June rainfall records were set from Virginia to New York, including DC’s wettest June day overall (6.11” on June 21, 1972).  In the Mid-Atlantic Region, Agnes brought record flooding and the storm had a death toll of more than 100.  Agnes subsequently had its name retired.

Alma (1966):  This was the last major Category 3 hurricane that developed in the Atlantic Basin during June.  At peak intensity, Alma had sustained winds of 125 mph when it passed over the Florida Keys.  It weakened, however, as it tracked north and ultimately made landfall as a Category 1 hurricane in the Florida panhandle.  Were a similar storm to occur now, the impacts would be much more significant since Florida’s population and coastal development have increased dramatically in the decades since Alma.

DC’s Unofficial Start to Summer

 

Great Falls is a good place to keep cool !

Meteorological summer officially got underway on June 1 and continues through August 31.  This is the first June that average daily high/low temperatures and precipitation will be measured against the National Oceanic and Atmospheric Administration’s (NOAA) new 30-year climate benchmarks for the period of 1991-2020.  This new data set replaces the previous 30-year period of 1981-2010. 

Consequently, there are significant changes as the Nation’s Capital has grown warmer and wetter over that last decade.  Average daily high/low temperatures now range from 81°/63° on June 1 to 89°/71° on June 30.  The previous averages were 80°/62° on June 1 and 88°/70° on June 30. 

Ten of the last 20 June’s have been warmer than average in the Nation’s Capital.  The trend for warmer than average weather over the last decade is in particular led to NOAA’s updated climate statistics.  DC’s warmest June temperature on record remains the sweltering high of 104° on June 29, 2012.

The Nation’s Capital also averages more June rainfall that it did previously.  The new June rainfall average of 4.20” is 0.42” greater than the 1981-2010 average.  Three of DC’s five wettest June’s (2006, 2013 and 2015) have occurred in the last 15 years.  June can also be a dry month as local residents experienced in 2017, when only 1.13” of rainfall occurred.  That made June 2017 DC’s third driest on record.

Although rare, the DC Metro Area can feel the impacts of decaying tropical systems in June.  Longtime Washingtonians may remember the record flooding of June 1972 due to the remnants of former Hurricane Agnes.  June 1972 now ranks as DC’s third wettest.  However, there isn’t anything currently brewing in the tropical Atlantic.

Another key trend in the DC’s Metro Area has been the disproportionate number of record highs in recent decades compared to record lows.  For example, the month of June has had 11 record highs in the last 20 years.  Meanwhile, you have to all the way back to June 22, 1992, for the last time the Nation’s Capital experienced a record low temperature.  A key reason for that is the increasing amount of urbanization and automobile traffic that’s enhanced the urban heat island effect.  The higher volume of traffic has also produced a larger concentration of greenhouse gases, which only serves to help intensify the “greenhouse effect.”  NOAA’s outlook for June 2021 is for warmer and wetter than average conditions in the D.C. Metro Area.