As seen in the Denver Post

We’ve all heard the saying that Denver and Colorado see an average of 300 days of sunshine per year. Well, this year (and probably every year to come) will not meet that criterion.

It’s a full-on myth that dates back to the 1870s that Colorado sees 300 days of sunshine per year. Nolan Doesken, a Colorado state climatologist who worked for the Colorado Climate Center for 40 years, said this is one of his favorite topics because of the unique history and blatant falseness.

While digging into this claim, Doesken found a New York newspaper from 1870 that had reference to the 300 days of sunshine in Colorado. The author of this article wasn’t a reporter but a publicist for one of the railroads in Colorado.

“The railroads were trying to advertise to the city folks back east of this marvelous climate out west which was previously called a desert that some people were scared to visit because of the Indians and the buffalo and other wild animals,” Doesken said.

Eventually, travelers took the bait and realized that the weather here is pretty darn great — at least compared to places like Cleveland and Chicago. But this marketing phrase had absolutely no legitimacy.

“There was no data whatsoever. People weren’t measuring sunshine back then. They didn’t even try this measurement until the 1890s,” Doesken said. So this claim to fame was just that — a claim.

Cloud measuring began in the 1890s to early 1900s. Data found that the number of clear to partly cloudy days averaged about 250, but this was based on an unknown definition of what cloud cover was. Still, this is less than the original 300-day claim. The phrase stuck and has been used as a marketing and travel tool ever since.

Cloud cover measurements were done visually until the mid-1990s and then the tracking became automated. The automation of cloud tracking did not measure any high clouds. It only measured low clouds which don’t accurately represent the full spectrum of clouds in different layers of the atmosphere. So, tracking cloud cover became harder to do as of the 1990s making it difficult to debunk the claim that we get 300 sunny days per year.

Doesken did an assessment (before the switch to automated cloud tracking in the 1990s) to find out how much sun is needed per day for there to be 300 days of sunshine. Turns out, if you consider just 1-hour of sunshine during a day to qualify as a sunny day, then you will have 300 days of sunshine per year in Denver. (Author note: I’m a meteorologist and I find it hard to believe that anyone thinks that just one hour of sunshine per day constitutes it being a sunny day. I would need at least five hours of sunshine, but that’s just me.)

For areas of the northern Front Range, there is an average of 60 days of completely overcast conditions – think drizzly, dreary or damp days, according to Doesken’s research. So, for the claim to be true, one has to consider a partly or mostly cloudy day to be a sunny day since technically the sun shined for a least an hour and although this is a stretch, it’s the only way to validate us having 300 days of sunshine per year.

The truth is that Colorado does see a lot of sunshine but whether or not a day is deemed sunny or cloudy is based on updated definitions by the National Weather Service and hourly observations.

  • A mostly clear or clear day is defined as cloud cover covering less than 25% of the sky.
  • A partly cloudy day is defined as cloud cover covering about 26 to 69% of the sky.
  • A mostly cloudy day is defined as cloud cover covering more than 70%  of the sky.
  • A completely overcast day is defined as cloud cover covering more than 88% of the sky.

Although the cloud data collected by the National Weather Service isn’t perfect, solar energy data can represent how much sun is shining down. This kind of solar energy is measured at close to 90 locations across Colorado by a network of agricultural weather stations. The data is raw and difficult to process though so not much research has gone into tracking amounts of incoming solar energy.

An interesting note is that cloud cover is calculated by the percentage of opaque clouds in the sky, not transparent clouds — and wildfire smoke falls under the transparent clouds category.

So although our skies have been filled with smoke lately, those smoky days have been categorized as partly to mostly sunny, according to the definition. This further skews the number of sunny days we have and makes it more difficult to track the actual number of sunny days.

“Alamosa is actually one of the sunniest spots in the state. Followed by areas near Pueblo and Rocky Ford. And believe it or not, Boulder is one of the cloudiest cities on the Front Range,” Doesken said.

Last year, Denver saw just 103 sunny days. The rest were partly to mostly cloudy. So far this year, we have only had 54 clear days as of Friday. You can do the math, but to hit the point home, we have more than 100 days left in the year and even if every day was completely clear, we’d barely even get half of the advertised number of sunny days this state boasts.

Sorry, Colorado — it’s not as sunny here as you thought!

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