Monday, May 8, 2023

Sunniest Ski Areas?

As much as people like to argue about whether or not ski area snowfall reports are legit, but perhaps there's more to argue about in the "day's of sunshine claim."  

Snow Brains recently published a top 7 list of the sunniest ski resorts in America.  Coming in at #1 was Palisades Tahoe with "more than 300 sunny days per year."

The 300 days of sunshine claim as been around for as long as I can remember.  When I was a kid, walking uphill both ways to school in sub-zero temperatures in upstate NY, I used to read promotional brochures from the Lake Tahoe area claiming more than 400" of snow and 300 days of sunshine and dream about how incredible the skiing must be there.  I mean, it must either be snowing or sunny!  What could be better. 


However, there are many things that are puzzling about that number. 

First, it is an annual number.  If you are a skier, you really want to know how often it is sunny during the ski season.  Winter is the cloudiest part of the year in the Tahoe area, whereas summer and early fall are less cloudy. Thus, the annual number is skewed by the seasonality of cloud cover.  

Second, sunny day is not defined.  Does it have to be bluebird all day?  If the sun peaks in and out it that good enough?  What if the mountain is shrouded in fog at the base and clear on top?  

For instantaneous observations, the National Weather Service defines sky coverage based on the opaque cloud coverage "octants" (divisions of eight) below.  


At what coverage does cloudy stop and sunny end? And, since cloud cover varies during the day, how does one deal with variability?  

Finally, what observations are being used?  Most ski areas do not collect sky cover observations and the closest observing stations that do are often at airports and not necessarily representative of what is happening on the mountain.  

I suspect these numbers have simply been cooked up with liberal interpretation of nearby airport observations that are not necessarily representative of on-mountain conditions.  Indeed, about a decade ago the Tahoe Daily Tribune published an article about a Tahoe area resident, David Antonucci, who runs and likes to set the record strait on Tahoe-area claims.  As described in the article Mr. Antonucci looked into the 300 days claim and suspects it is based on observations from the Tahoe Valley Airport. 

“I think where it came from is, at the Tahoe Valley airport, they used to make sky observations. So, I had some records from 21 years of observations that if you multiplied it all out it comes out to about 300 days. And I think what’s said there is there’s 300 days in which there is some sunshine. But I was also able to find probably actually a little bit better statistics. I went to a document called the Climate Atlas of the United States and it has the total number of hours of sunshine in a particular area. So, here at Lake Tahoe we have 4,446 hours of daylight each year and, of that time, at least 3,400 hours there’s sun shining, so that works out to 76 percent. Seventy-six percent of the time during the daylight hours the sun is shining, on average, is probably a better way to say it. You say ‘300 days,’ you think, ‘Oh, that was a day which is all sunny all day long,’ and it may not have been; it may have been sunny part of the day and then cloudy. I was not able to find much in the way of any data speaking to actual days of sunshine or cloudy weather, but for our region it’s probably not too far off. Reno has 251 days of clear and partly cloudy weather, Blue Canyon has 238 days of clear and partly cloudy days, so you can see it’s possible that Tahoe is higher, maybe under 300. It seems like it could be a reasonable number, but it should not be interpreted as that’s a whole day of just sunshine and no clouds.”

So, if 300 days of sunshine seems too good to be true, that's because it is.  

This isn't to say that the Tahoe-area resorts, and other Sierra resorts like Mammoth don't get a lot of sunshine compared to many other areas.  They might even be the sunniest resorts.  However, the 300 days claim is inflated. 

1 comment:

  1. Ide be interested to see a list like this but with the average aspect direction taken into account