Thursday, August 1, 2019

July Was Hot, but Thankfully Is in the Rearview Mirror

Yesterday was a wonderful last day of July.  Temperatures at the Salt Lake City International Airport topped out at 92˚F, but with rain moving it, it was drippy and 69˚F by 6 PM.  It was wonderful to feel the cool air and let my skin soak up the moisture.

It was my impression that July wasn't horrible.  This might reflect the fact that I lived through the European June heat wave or that we did have the occasional cool day to break up the July low-variability monotony.  However, a look at the numbers shows that the average temperature at the Salt Lake City Airport this July was still remarkably warm compared to the past.  It rates as the 9th warmest since 1874.  And, just to illustrate that you aren't living in your grandparents climate, there wasn't a single July as warm as this one until 2003.  In other words, this July was hotter than any July on record in the late 19th and 20th centuries.

Source: NOAA Regional Climate Centers
Further, the 12 warmest Julys have all occurred in the 21st century.  Brutal.

Elsewhere in July, probably the two biggest stories globally have been the extreme warmth observed in late July in Europe, during which all-time high temperatures were recorded in Belgium, Germany, Luxembourg, the Netherlands, and the United Kingdom, as well as significant melting events on the Greenland Ice Sheet.  The World Meteorological Organization (WMO) provides a summary here.  June 2019 rated as the warmest on record, and I suspect July will rate amongst the warmest if not the warmest.

Thus, it's good to have July in the rearview mirror.


Posting time series from Heber City and Tooele for comparison and to illustrate that similar trends are seen elsewhere and in less urbanized areas, although the urbanization may exacerbate things in Salt Lake.  


  1. I've mentioned this before, and I don't mean for it to be in any way combative. When I see such graphs, the first thing that pops in my head is "that looks like urban heat island effect much more than global warming, that's why I bet the airport this year was hotter than in the 19th or 20th centuries".

    Are there any other locations within 100 miles or so that has comparable data that helps avoid UHI?

    1. UHI is a possible contributor, but it does't explain it all. Stations nearby with very long records and limited missing data that make for a good comparison are pretty limited, but I'll post Heber City and Tooele at the end of the blog post in a minute.

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    3. Thanks! I definitely appreciate it. This topic sent me down a rabbit hole, and I found this paper helpful, especially charts 1, 2, and 3.

      Bias warning: SPPI definitely has a non-neutral agenda, and the paper is not peer reviewed. However, those charts seem to get to the heart of the issue in a non-biased way.

    4. Brad:

      Thanks. We don't really have good quantification of the UHI effect in Salt Lake and how it has affected temperature trends specifically at the airport. That being said, I don't doubt it is a contributor. I have blogged about this previously: