We already know that this summer has been hot and that we have had very few days with a below average minimum temperature (only one day in July and August has had a below average minimum temperature, see previous post). But did you also know that the day-to-day fluctuations in minimum temperature have also been much smaller than usual?
To illustrate this, Trevor Alcott sent me the analysis below showing the average (mean) and standard deviation of minimum temperature at the Salt Lake City International Airport during the heart of summer (1 July to 15 August) since 1958. This year not only has the highest average temperature, but by far the lowest standard deviation.
|Source: NCDC/Trevor Alcott|
However, if you look at the graph below, you will notice that before 2011, the lowest standard deviation in any year was about 4ºF. Since 2011, however, we've seen standard deviations at or well below that level.
It is my understanding that the observing system at the airport (known as ASOS) was moved about three years ago and I wonder if this could be playing a role in the decline. This year has been boring, with limited weather variability, but the remarkably low variability in minimum temperature at the Salt Lake Airport might partly reflect characteristics at the new instrument location. More digging is needed to test this hypothesis.