Thursday, July 21, 2016

An Impressive Heat Wave Despite No Maximum Temperature Records

This may sound like a broken record given that I've mentioned it several times this summer already, but there's more to heat waves than maximum temperatures.  Maximum temperatures get the most press, but minimum temperatures strongly affect human comfort, animal and plant health, energy demand, and even air quality.

Bars in the graph below show the range of temperature (bottom = minimum, top = maximum) each day this month compared to average (green shading), record maximums (top of red shading), and record minimums (blue shading).  Over the past 3 days the maximum temperature has fallen short of records by a few degrees, but the extreme warmth of the period is evident in minimum temperatures that are remarkably high.

Source: NWS
The minimum temperatures the past three days were 81ºF, 77ºF, and 79ºF.  Plus, our overnight minimum last night was 79ºF.  The 81ºF is the highest minimum temperature ever observed in Salt Lake City, as summarized nicely by the graphic below from the National Weather Service.

Source: NWS
The 79ºF yesterday and the 79ºF this morning (assuming it holds as the daily minimum through midnight, which is likely), would tie for the 4th warmest.  Three days in a row of 77ºF or higher is the first on record, and it appears today will add a fourth.

Bottom line: There has never been a string of warm nights and high minimum temperatures like the one we are experiencing this week.  

The recent warm spell has also put us back in first place for hottest summer on record so far.  Through yesterday, the average temperature since June 1st was 78.9ºF, just ahead of the similar period in 2013.

Source: NOAA Regional Climate Centers
The toxic algal bloom in Utah Lake has been getting much attention in the news of late (see this Salt Lake Tribune article).  I've been avoiding touching it (figuratively and literally!), but thought I would comment on it here.

I am unaware of a long-term lake-temperature record for Utah Lake, but shallow lakes typically have temperatures that are close to the recent average atmospheric temperatures in the surrounding area.  Long-term temperature records in Utah County are spotty, but the Provo-BYU record closely mimics the Salt Lake City record above, with recent years being warmer than earlier in the century and a long-term trend over the past 4 decades.  Similar to Salt Lake City, the summer so far has been the warmest on record at Provo-BYU, although by only 0.4ºF over 2015.

Source: NOAA Regional Climate Centers
So, this summer has so far been one of unprecedented regional warmth, although the difference relative to the first part of summer last year is fairly small.  The warmth this year is probably a contributor, ultimately it must be considered with other factors (e.g., phosphorous and nitrogen loaded runoff, sunshine, etc) to understand why this year's bloom is so severe.


  1. You don't think all that development along the Utah Lake shoreline isn't a factor? Twenty years ago, the city of Saratoga was a town. Geneva Steel has been leaching heavy metals into the lake for decades, it should be a Superfund site.

    1. My list of factors above is a partial one and not meant to be complete.

  2. Lightning visible across the lake! Yay! It's still very hot, but it's nice to see.

  3. Don't let the fact that this is the warmest summer so far get in the way of the 2 News weather person saying that we've been spoiled so far with this nice summer, apparently because we aren't on pace to break the number of 100+ degree days.

  4. I love Utah (we've lived here 7 years), but I only like it in July and early August. Part of that is because of the minimum temperatures. When I lived on the Front Range of Colorado (roughly +1,000' in altitude compared to the Wasatch front), even really hot days would cool off overnight, which I think changes how hot it "feels" considerably. Fall cannot come soon enough for me.