In a normal year, Denver will see an average of 46 days of 90-degree heat. That number has been ever-increasing as our summers have been getting warmer and warmer over the years.
When we talk about heat in Denver, it’s usually customary to reference the number of 90- and 100-degree heat days to give an idea of where we stand in terms of how hot a season has been.
This year, much like recent years, has provided the Front Range with a huge surplus of days with intense heat. So far, through mid-September, Denver has felt 90-degree heat on 57 days, well above the normal 46 days. Nine out of the top 10 years with the most days of 90-degree heat have happened since 2000.
Denver has felt 100-degree heat for 5 days this year which ties the city for third place for the most number of 100-degree days behind 2012 (13 days) and 2005 (7 days). Interestingly, prior to 2000, it was pretty rare to feel 100-degree heat in the city. From 1872 (when weather records began to be collected in Denver) to 2000, Denver averaged zero days of 100-degree heat. It just wasn’t the norm. From 2000 to now, Denver has averaged 3 days of 100-degree heat per year. A notable upward trend.
Data from ClimateCentral shows that Denver’s average summer temperatures have warmed by 2.6-degrees since 1970 and we experience 17 more days of 95-degree heat per year than the 1970s. This trend of hotter weather is a factor that should be realized when planning for the future. There is simply more hot weather expected now than there was before.
On a national level, the United States just experienced a hotter summer (June-August) than the Dust Bowl of 1936. California, Nevada, Oregon, Idaho and Utah all had their hottest summer on record this year. Colorado as a whole had its fourth warmest summer on record and Denver ranked third for hottest summers ever with an average temperature of 74.6-degrees.
The first half of September 2021 ranked as the hottest start to September ever – further elongating our summer heat season. The elongation of summer heat is also a trend that meteorologists and climatologists have been watching closely. With 80- to 90-degree heat lasting longer into September and even October, it is not only elongating the summer season but shortening the fall season.
In Denver and along the Front Range, although we’ve had a few cool downs, more above-average heat is expected before the end of the month.