Copper storm totals 11/10-11/15

This last week has seen a lot of snow fall over the state. Almost all forecasts from all the sources I look at under-predicted. Not only did they under-predict storm totals, they under-predicted almost every single day! I’m going to look at Copper Mountain again today.

Every morning I check forecasts for the next 24 hour snow predictions. I do this because 24 hour predictions should be the most accurate. I would like to update in the evening, so I can know whether to head to the mountain┬áthe night before, but forecasts are updated in the morning. C’est la vie.

So let’s look at how the NWS and Opensnow did…


As you can see, there weren’t a lot of good snow forecasts there. Basically, what I think we’d all like to see is not so much perfect forecasts, but accurately predicting powder days. That is, if a powder day is predicted then we’re happy if it’s a powder day even if the total amount predicted is off by a few inches. Conversely, if a non-powder day is predicted then it better not be a powder day, because we’ll miss it!

For me personally, missing a good powder day is worse than having a predicted powder day but not receiving a lot of snow. Why is this? Because if a powder day is predicted, then I’m probably going to drive to the mountain. If it doesn’t snow, then at least I’m still boarding. If a powder day isn’t predicted, then I may or may not drive to the mountain, but probably not. And therefore, I’d miss a good snow day.

Definitions of what a good powder day is vary between people, but for me 42″ over 6 days qualifies. I actually didn’t get out because I had other work. I didn’t mind because it’s so early in the season. If it was January and the base was good, I would have likely skied all five days had I been up there. But would I have made the trip based on the forecasts? Likely not for the 10th through the 12th. Even with 7″ in the first two days, the next days forecast was only 1.89″ or 2.5″. That’s hardly enough for a good day. And I would have not been happy when 8″ fell!

The forecasts for the next day (7.28″ and 6″) would have seen me drive to the mountain. I would have been surprised to see so much new snow, but I would have already been there. So even though the forecasts were off by 4-5″, I still consider that a much better forecast than the previous day when the errors were similar, but they missed predicting a powder day.

One thing that sticks out is that every forecast was an under-prediction. What caused this bias? I mean, NWS under-predicted by over 50%! That’s absolutely terrible. Opensnow did a little better, but still every day was under-predicted.

It’s early winter, so maybe everyone is a little rusty from the summer. That’s my hypothesis anyway.

My name is Nathan Johnson and I have a Masters degree in Meteorology. I also snowboard and live in Boulder, Colorado.I have a strong desire to see precise, accurate snow forecasts. It is my hope that independent validation and verification leads to better forecasts.

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