Turns out we don’t get 300 days of sunshine

Despite the saying that Colorado receives an average of 300 days of sunshine per year, this year — and for probably years in the foreseeable future — will not meet that number.

It’s a myth that dates to the 1870s. Nolan Doesken, a state climatologist who worked for the Colorado Climate Center for 40 years, said this is one of his favorite topics because of the 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 the benefits of the weather here — at least compared with places such as Cleveland and Chicago. But this marketing 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 300day 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 measured only 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. If you consider just one hour of sunshine during a day to qualify as a sunny day, then you will have 300 days of sunshine per year in Denver.

For the northern Front Range, there is an average of 60 days of completely overcast conditions — 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 because technically the sun shined for a least an hour. Although this is a stretch, it’s the only way to validate the state 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 clouds covering less than 25% of the sky.

• A partly cloudy day is defined as clouds covering about 26% to 69% of the sky.

• A mostly cloudy day is defined as clouds covering more than 70% of the sky.

• A completely overcast day is defined as cloud cover over 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.

“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.

But if we’re counting only clear days, Denver saw 103 of those last year. So far this year, we have had 54 clear days as of Friday.

And with more than 100 days left in the year, even if every day was completely clear, we would get about half of the number of clear days the state boasts.