Saturday, July 16, 2016

First Half of Summer Tied for Hottest Ever in Salt Lake

We are now half way through meteorological summer and the average temperature for June 1 – July 15 is tied with the same periods in 2013 and 2015 as the hottest ever in the Salt Lake City area with an average temperature of 78.1ºF.

Source: NOAA Regional Climate Centers
Both the average minimum and average maximum temperatures were well above the long-term average for the period, although it is the minimum temperatures that have really stood out compared to past summers.

Source: NOAA Regional Climate Centers
Source: NOAA Regional Climate Centers
The traces above are based on records from Salt Lake Area stations, but exclusively records from the Salt Lake City airport beginning in 1928.  The impact of the station shift is very clearly illustrated by the abrupt drop in minimum temperature from 1927 to 1928. The airport is one of the coldest places in the Salt Lake Valley at night and shifting to that location yielded much lower minimum temperatures compared to the previous observing site.

The climb in minimum temperature since then likely reflects several factors.  One is global warming as minimum temperatures are rising faster than maximum temperatures on a global scale.  It is also likely that urbanization of the Salt Lake Valley is having an effect, especially since the flow at night is typically southeasterly at the Airport and originates in developed areas. These effects are most apparent in the summer, especially from late June through July, when the day-to-day weather variability in northern Utah is the smallest (on average) of the year.  It is during this period that the long-term warming trend is most apparent.

The growth in minimum temperatures has important implications for human health and comfort.  Imagine living in the Salt Lake Valley in the 1940s and 1950s.  For the June 1 through July 15 period, the average minimum temperature during that era was about 55ºF.  That's pretty comfortable and allowed for efficient natural cooling of your home.  Over the past 10 years, its about 60ºF and over the past 2 summers its 65ºF.  In urban areas, you can expect it to be warmer at night than that.

Welcome to Hot House Salt Lake.  Through global warming and urbanization, we are having a major impact on the climate and livability of the Salt Lake Valley.

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