Reno’s sweltering summer was a record-breaker

• Reno's climate keeps getting warmer
• It's part of broader, global trend
• Human-induced global warming and urban heat island combine to produce heat records
• Vast majority of Reno's 15 warmest seasonal records happened since 2001

Reno’s sweltering summer was a record-breaker, in more ways than one.

The average daytime high for June, July and August, what’s known as climatological summer, was 93.6 degrees.

That’s the hottest summer average high ever recorded in Reno, breaking the record of 93.3 degrees set in 2017.

Summertime also included a record streak of 56 consecutive days where the temperature reached 90 degrees or greater, which ended Aug. 25.

There were also 20 days on which the daily high reached 100 degrees or greater, the most recent on Aug. 19. The previous record for 100-or-more days was 16, set in 2017.

In additions to the records, there were some near-records.

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The mean average summer temperature, which is an average of daily highs and lows, was 76.9 degrees. That’s the second-highest recorded in Reno, just behind the record of 77.2 degrees in 2017.

“It accounts for the entire day, not just the hottest time of the day,” said Dan McEvoy, a climatologist at the Western Regional Climate Center in Reno.

The average minimum temperature, a reference to nighttime lows, was 60.1 degrees, just short of the record of 61.2 degrees set in 2017.

“The trend is continuing, where the overnight minimums trend has been much more significant than the daytime maximum,” McEvoy said.

5 hottest Reno summers

Rank    Year        Mean average temperature*

1            2017      77.2 degrees

2            2018      76.9 degrees 

3            2007      76.2 degrees

4            2013      75.4 degrees

5            2014      75.3 degrees

* Mean average temperature combines daily highs and lows

Part, but not all, of the overnight trend is due to the urban heat island effect, which refers to how pavement absorbs heat by day and releases it at night.

The trend is more pronounced in urban areas such as Reno and exacerbates the overlying trend of human-induced global warming due to fossil fuel burning.

“That’s part of it but we also have the fact we’re not getting any help from the larger climate,” said Ben Hatchett, a climate researcher at Desert Research Institute who has studied the urban heat island.

Scientists can separate the heat island effect from global warming by looking at temperatures in rural or less urbanized places, such as the Lake Tahoe basin which, like the planet, is also warming at greater-than-natural rates.

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The mean average in Tahoe City was 62.4, slightly higher than the previous record of 62.3 set in 2017.

The average overnight minimum was 46.2 degrees, the second warmest recorded just behind the 2017 record.

The average daily high at Tahoe City was 78.6, the seventh highest on record.

The summer numbers are part of a broader trend of human-induced global warming.

Seventeen of the last eighteen hottest years recorded in 136 years of recordkeeping have occurred since 2001, according to NASA.

In Reno, 12 of the 15 hottest summers measured by daily high have happened since 2001. When it comes to warm overnight lows, the 15 warmest have occurred since 2001. And the 15 overall warmest summers, as shown by an average of daily highs and lows, have all occurred since 2001.