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The suns sets behind the Rocky Mountains after daytime high temperatures reached above 90-degrees Monday, June 26, 2023, in Denver. (AP Photo/David Zalubowski)

Last Friday, the daily high temperature in Denver flirted with a mark not seen so far in 2023: 100 degrees Fahrenheit.

This year could end up being the first since 2015 without a 100-degree day in the state capital. But the 99-degree high Sept. 1 was still a record for the day — and that is anything but an anomaly in recent years.

Inspired by last week’s 99-degree record-breaker, we decided to chart when each of Denver’s 366 daily records for high and low temperatures was set, going back 151 years to when such records began being kept. (366 and not 365 to account for the record readings on leap days.)

As you can see, the record lows are fairly evenly distributed, with a noted lull in the 1920s, ’30s and early ’40s. But record highs are concentrated in more recent years.

Nearly 50% of Denver’s daily record-high temps — 178 of 366 — have been set since 2000. One-third have been set since 2010, and more than 12% — 46 daily record highs — have been set since 2020.

For comparison, about 19% of Denver’s daily record-low temps have been set since 2000, and about 4% have occurred since 2020.

Last week’s record temp toppled a mark that stood for only four years. It was the fourth record-high temperature set so far in 2023, to go with five record-low temperatures.

And, despite what has felt like a pretty mild summer in Denver, the average daily temperature between June and August actually fell right in line with long-term averages, ranking it the 80th-coolest summer in 151 years, according to 9News.

These readings do come with a caveat, though. While they are all taken from Denver’s weather station of record, the location of that station has moved around a bit.

From 1872 through 1948, the station was located at the National Weather Service’s downtown Denver office. It then moved to an office at Stapleton Airport, in what is now Denver’s Central Park neighborhood, until February of 1995. After that, it moved out to Denver International Airport.

This movement, occurring within a span of about 18 miles, from an urban center to a residential neighborhood to an open grassland, has an impact on the continuity of the data — meaning that, from a scientific perspective, extrapolating trends from this data is not statistically valid because the current station might be in a location that is slightly hotter or colder than a previous one.

“The whole situation with the lack of a good, long-term climate station for Denver is a common source of questions and frustration for folks in our business,” Russ Schumacher, the director of the Colorado Climate Center at Colorado State University and who serves as the state climatologist, wrote in an email.

There is still a weather station maintained in the Central Park neighborhood, though. Schumacher looked at readings taken from that weather station and compared them to ones taken at DIA. He found nine high-temperature records set at DIA since 2000 that would not have been records if the Central Park station reading were used.

“But there’s still a clear increasing trend,” Schumacher wrote.

The average annual temperatures at the Central Park and DIA stations “is essentially identical,” Schumacher said, but which location is warmer or colder can vary by season. DIA often has warmer overnight lows than Central Park, Schumacher said. And a chart that Schumacher produced for The Sun showed some years since 2000 when the Central Park station would have set more high-temperature records than DIA.

So, while the data is beyond muddy, Schumacher said it is likely correct that nearly half of Denver’s record-high daily temperatures have occurred since 2000.

“Yes, it’s warming, and, yes, Colorado is getting more frequent record-high temperatures,” Schumacher wrote.

In short, we are presenting this data to show proof of that trend — official heat records are being broken more frequently in Denver — while acknowledging there’s a lot of complexity at work.

We created the searchable database below so you can look up the official record daily high and low in Denver for any day. But note that the figures are only current through today (Sept. 7, 2023). That means, as climate change warms the state and leads to more extreme weather, this database won’t be updated when, inevitably, new record daily temperatures are set.

Editor’s note: This story was updated at 10:00 a.m. on Sept. 12, 2023, to include comments from Colorado state climatologist Russ Schumacher and to address how changing locations of Denver’s official weather station has affected the reliability of the official historical record.

John Ingold is a co-founder of The Colorado Sun and a reporter currently specializing in health care coverage. Born and raised in Colorado Springs, John spent 18 years working at The Denver Post. Prior to that, he held internships at...