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Is 300 Days Of Sunshine In Colorado A Fact Or Just Good Marketing?

DENVER (CBS4) - It's long been said that Colorado receives 300 days of sunshine each year.

Is there truth to that or is it just an urban myth?

To find out we consulted the Colorado Climate Center at Colorado State University.

Let's start with the formal definition for "days of sunshine."

"The problem is there is no official definition," said Nolan Doesken, Colorado State Climatologist. And that means there is no data set to consult for answers.

In Colorado there are three locations that operate a device called a "sunshine switch" that measures sunlight by the minute.

They're located in Pueblo, Denver and Colorado Springs.

But the instruments must be constantly cleaned and calibrated to be effective and that rarely happens.

The Colorado Climate Center did a study in the 1990s based on sunshine switch data and found that for Denver, if you count every day when the sun came out for at least one hour, then you could come up with an average of around 300 "days of sunshine" each year.

But most people would probably not consider an hour of sunshine a "sunny day."


The National Weather Service has established a criteria for determining if a day is clear, cloudy or partly cloudy.

If cloud cover each day is 30 percent or less then it's considered to be a clear day.

If cloud cover is 80 percent or more it's a cloudy day.

Anything in between would be recorded as a partly cloudy day.


Based off the National Weather Service definitions, the climate center's study found that Denver can typically count on having about 115 clear days, 130 partly cloudy days and 120 cloudy days each year.

The numbers are pretty similar statewide although the number of clear days in a place like Grand Junction are slightly higher than Denver.

"The fact is, here in Colorado and much of the Rocky Mountain region, there are relatively few totally clear days but a whole lot of days when the sun peeks out at least a little. Therefore, we tend to brag about our sunshine but mislead folks along the way," said Doesken.

So it basically all depends on how you choose to interpret what exactly "300 days of sunshine" really means.

Meteorologist Chris Spears writes about stories related to weather and climate in Colorado. Check out his bio or follow him on Twitter @ChrisCBS4.

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