In the last post, Tony Crocker offered some insights into what he’s been seeing at a general level in his snow-tracking pursuits. Here, I present some of the actual findings.
In e-mail correspondence, he clarified the calculations of the numbers and provided some additional thoughts. While this isn’t a guest post, but a summary of our correspondence, all work is Tony’s and most of the pertinent observations come from him.
Tony has broken North America into 8 regions. He used his own judgment in defining the regions, but in his words “My regional definitions are somewhat arbitrary (though most skiers would consider them reasonable), and the regions are big enough that within a region there can sometimes be some areas with good seasons and others with bad seasons in the same year.” The regions are as follows:
1 – California
2 – Pacific Northwest
3 – Interior Canada
4 – U.S. Northern Rockies
5 – Utah
6 – Northern & Central Colorado
7 – Southern & Western Colorado
8 – Northeast
Within each of the regions, the data point is “Percentage of snowfall relative to normal.” The final data point for the region is a straight average of all the observations in that region. The Data is tracked as far back as 1970-71 season. Some of the years 1970-75 had significant snowfall, but he excludes those years in some calculations. The main reason for excluding the data is the low number of data points available.
Data Considerations: (1) Spread of resorts within region could cause weighting issues which do not appear to have been considered; (2) number of resorts with good information can differ from year to year; (3) the expected snowfall will change from year to year as data is added, but Tony recalculates historical data to account for that.
*Most variable region = California shows a standard deviation of 31%. The most consistent, least variable, data is the Interior of Canada (15%). Overall North America had a standard deviation of 13% over the time frame.
*The longest trend, including the less credible data of the early 1970s shows an overall trend from 1970 – 2009 of -2.9%. However, Tony ran trends from 1972, 1975, 1982, 1987, and 1992 that were all positive. The highest trend in overall North American snowfall, in fact, is since 1975, at +9.8%.
*Every single region has a positive trend since 1975. Some regions show some negatives during the shorter trend time-frames. The region with the largest trend is the Pacific Northwest, +21.1% since 1975. But in a show of how volatile results can be, this same region actually has the largest negative trend back to 1970 because of high snowfall early in that decade.
*There is some significant correlation in snowfall between many regions, though not all. It’s not necessarily surprising that the Utah and Colorado regions are very highly correllated. Other areas of high correlation (over 50%) are: California/U.S. Northern Rockies; California/Utah; California/Southern & Western Colorado; Pacific Northwest/Interior Canada; Pacific Northwest/U.S. Northern Rockies; Northern Rockies/Utah; Northern Rockies/Both Colorado Regions.
*Negative correlation is indicated between: California/Canadian Rockies (most distinct negative correlation); Canadian Rockies/Utah; Canadian Rockies/South & West Colorado; California/Northeast.
I asked Tony, based on his experience and observation, what are his main conclusions. The following is his response:
1 – No trend in snowfall over the past 35-40 years in North American ski areas despite rising temperatures during most of that period.
2 – Rising temps don’t necessarily affect precipitation, but do affect the rain/snow line. This is not yet an issue at almost any ski area in North America (Whistler base and Snoqualmie might be exceptions) but there are other ski regions of the world (Australia comes to mind) where it might be more serious.
3 – data is very volatile and it’s dangerous to claim trends based upon typical measuring periods like 5 or 10 years.
I’m providing three charts: the overall North American chart, the California chart and the Pacific Northwest chart. On the Pacific Northwest chart, keep in mind that from 1976 forward the trend is largely positive, but from 1971 forward it is negative. California shows the volatility of the region, and the difficulty in being able to make grand assessments in the short term regarding snowfall and temperature.
Thanks for the information, Tony.