Monday, August 1, 2016

Mother Nature's Natural AC Can No Longer Do the Job in July

July is in the rear-view mirror and not a moment too soon.  Despite the heat of the past couple of weeks, it enters the record books with an average temperature of 83.1ºF, good for 4th warmest on record, behind 2003, 2007, and 2013.

Source: NOAA Regional Climate Centers
Preventing us from the record was the July 10-11 cold surge.  Surely you remember the maximum temperature of 76ºF on July 11?  Ah, the good old days.  

Although July wasn't a record breaker, the average temperature for the first 2/3 of summer (June–July) was the hottest on record, topping 2013 by 0.6ºF.  

Source: NOAA Regional Climate Centers

During June and July we saw 14 days with a maximum temperature of 100ºF or higher.  That ties for the 5th most on record.  

Source: NOAA Regional Ccimate Centers
As we have noted before, however, it is the minimum temperatures that are bringing true misery to the region.  The chart below shows the number of days in June and July with a minimum temperature at or above 75ºF.  This year's 11 is the highest on record.

Source: NOAA Regional Climate Centers
If we use 70ºF instead, this years June and July ranks 2nd behind 2013. 

Source: NOAA Regional Climate Centers
The graphs above show that we entered a new summertime climate regime in the first part of the 21st century.  At the Salt Lake City airport, the 9 warmest Julys on record all occurred since 2002 and nights are clearly much warmer than they used to be.  How much of this is due to global warming, regional climate variability, urbanization effects, or characteristics of the Salt Lake City airport observing site warrants a deeper investigation than I can do for this blog post, but one thing is clear.  Mother Nature's natural air conditioning can no longer do the job in the Salt Lake Valley in July.  


  1. What happened in Jun/Jul 1993? You can plot up the 500mb geopotential height mean and anomaly for that period using the webpage here:

    It's interesting that the mean field shows a trough over the West, and I have to think this is extremely rare. The anomaly field shows northern Utah in the base of a broad trough. It's still hard for me to imagine a Jun/Jul period with a mean temperature of 67 degrees... we've been hard pressed to have minimum temperatures below that lately.

    Given that my first 3 summers here were '09, '10, and '11, it seems like the heat has really been on during the last 5, but of course it's just reverting to the trend.

    1. You are right that it is hard to keep a trough over the west in July, but it would be nice if it happened again!