Data Sense: Steamboat’s high Opening Day snow depth bodes well for December
Strong early season snowfall has resulted in a robust snow depth level in Steamboat to start the 2013-14 ski season.
When Steamboat Ski Area opened on Wednesday for Scholarship Day, five lifts and 57 trails were ready for action. As of Wednesday, Steamboat Ski Area was reporting 87.5 inches of snowfall to date and a 26-inch base. The measured snow depth at the nearby Rabbit Ears SNOTEL site maintained by the U.S. Department of Agriculture’s National Water and Climate Center was 28 inches. This translates to 6.9 inches of snow water equivalent, or SWE, a more useful measure for data comparison purposes. This year’s Rabbit Ears SWE level is 6.9 times the drought-stricken 2012 SWE level of 1 inch, which was the lowest level since measurements became available in 1986. As it turns out, this year’s SWE total actually is higher than the measured levels on the same day for 23 of the past 27 years between 1986 and 2012.
But what exactly does the opening day snow depth level tell us about the prospects for high snow depth levels for rest of the ski season at Steamboat?
Before answering this question, it’s important to remember that forecasting any complex system is extremely difficult. This caveat is further amplified when it comes to weather forecasting because weather patterns are extremely complex and notoriously volatile. Nonetheless, an examination of the daily historical snow depth data at the SNOTEL Rabbit Ears site since 1986 does yield some very interesting information that we can use to consider likely snow depth levels for the rest of the year. Indeed, the historical data tell us that this year’s high early season snow depth total indicates that the snow depth level through the end of the calendar year is likely to be above average.
By examining the SWE level Nov. 27 and the SWE level Dec. 31 for each year, we can determine if there is a positive correlation between the two data points. A positive correlation between two data points tells us that if one rises, the other likely will follow suit. It turns out that the correlation between the Nov. 27 SWE level and the Dec. 31 SWE level during the past 27 years is 70 percent. This means that 70 percent of the differences in the end-of-calendar-year snow depth level at Rabbit Ears throughout the years can be explained by simply looking at the differences in the snow depth level Nov. 27. Higher snow depth on the ski area’s opening day does translate to higher snow depth at the end of the calendar year.
What’s really interesting here is that opening day snow depth levels impact end-of-year snow depth in two distinct ways. First, the obvious impact is that by starting at a higher base level on opening day, the year-end level is likely to be higher. On average, 4 inches of SWE are added to the snow depth between Nov. 27 and the end of the calendar year. Second, during those years with above-average snow depth on Nov. 27, the amount of snow depth added through the end of the calendar year also is above average. Thus, high opening day snow depth is in an indicator of above average snowfall in December. Based on this analysis, we can predict that the SWE level at Rabbit Ears on Dec. 31 will be 11.75 inches — well above the 27-year average of 9.31 inches.
The predictive power of the opening day snow depth declines for each subsequent month after December. The correlation between the Nov. 27 snow depth and the Jan. 31 snow depth is about 50 percent. The correlation between the Nov. 27 snow depth and the March 31 snow depth is about 40 percent. All of this analysis tells us that while strong snow depth levels on opening day bode well for the rest of the calendar year, they don’t provide as much information about how the remainder of the ski season is likely to unfold.
The bottom line here is that because this year’s opening day snow depth totals are high by historical standards, the chances for above average increases in snow depth in December are higher. Mother Nature will determine what happens after that — and the current snow depth levels provide fewer clues about what she has in store for 2014.
Brandon Owens is an independent contractor who performs data analysis for Yampa Valley Data Partners.
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