Record-Setting Heat ?

The Nation’s Capital set a new record for highest total number of 90° days during the month of July.  Yesterday’s high temperature of 93° was the 26^th day of 90° heat since July 1 and that broke the previous record of 25 days set during July 2011.  It’s also DC’s record for most 90° days in any month.  What has made this month’s heat unusual is the lack of extreme heat – no record highs or 100° heat.

It’s remarkable that 31 of the last 33 days have featured high temperatures in the 90s without any triple-digit heat, dating back to June 26.  With the exception of July 24, every other day this month has been warmer than average in Washington, D.C.  These consistent above average temperatures put July 2020 in position to finish among DC’s four warmest July’s on record. 
 

July 2020 finishing as one of DC’s hottest months on record is quite a feat all by itself.  However, making it even more interesting is that the existing list of the five warmest July’s have all had at least one day of 100° heat.  For example, during July 2012 there were eight days when high temperatures reached the 100s.  DC’s previous record for most 90° days of 25 from July 2011 is also significant since that remains DC’s warmest July.  It finished warmer than July 2012, despite having fewer days of triple-digit heat (five days vs. eight).  The difference, however, were warmer overnight low temperatures in July 2011 vs. July 2012. 
 

There will likely be a tangible difference in average low temperatures at National Airport when the National Weather Service updates its running 30-year average of temperatures at the end of the year to reflect the period of 1991-2020, thus replacing the current period of 1981-2010.  Overnight low temperatures have been warmer than average on all but two days since July 1, when they fell to the daily average.  According to NOAA, DC’s lowest temperature this month of 71° is its warmest monthly low temperature on record.  If Washingtonians don’t experience a temperature below 71° before the end of the month, then that will be another warm weather record set in July 2020.

This month is well-positioned to finish as DC’s third warmest July.  DC’s average temperature (combining daily high and low temperatures) through July 28 is 84.1°.  Some minor fluctuations above or below that are possible during the final few days of the month, but not enough for it to catch July 2011 for first place at 84.5°.  

DC’s Warmest July’s By Average Temperature (Source: NOAA)

1.  84.5° (2011)
2.  84.1° (2020 – as of July 28)
3.  84.0° (2012)
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)

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DC’s Most 90° July Days (Source: NOAA)

1.  26 (2020 – as of July 28)
2.  25 (2011)
3.  24 (1993, 1987)
5.  23 (2016, 1988)
7.  22 (2019, 2012, 1999, 1994)