Skiers hoping to use the El Niño Southern Oscillation cycle to predict snowfall at Purgatory Resort may want to think again.
The binary El Niño/La Niña weather patterns can be a tempting source of information for skiers in search of a crystal ball that will forecast the winter ahead. But this past winter is a telling anecdote that, at least at Purgatory, the ENSO cycle may be a poor guide. And that conclusion is supported by a recent analysis done by Fort Lewis College student Brooke Grover, 22, who just completed a senior capstone project examining Purgatory Resort’s historical snowfall data.
This winter, the third consecutive La Niña cycle, should have brought colder, drier weather. Instead, it yielded the fourth-highest recorded snowfall in the last 55 years.
Data collected by ski patrol indicates a total of 336.5 inches of snowfall this season, which is well above the average seasonal snowfall of 232 inches.
The unreliability of La Niña/El Niño weather systems in predicting Purgatory’s snowfall is a trend, according to Grover’s analysis.
Typically, El Niño cycles bring warmer and wetter weather conditions to the Western U.S., increasing snowfall. Purgatory has credited the patterns for good ski conditions in the past.
But Grover hypothesizes that Purgatory’s unique geographical setting, located at the convergence of a high desert and the San Juan Mountains, is responsible, at least in part, for the way that atmospheric rivers affect the area’s snowpack more than the ENSO cycle.
These narrow bands of high-moisture air transport and release high volumes of precipitation and were largely responsible for this year’s ample snowfall. While they are loosely correlated with the ENSO cycle, Grover’s analysis shows that the ENSO cycle is nonetheless a poor predictor of seasonal snowfall.
Strong El Niño years, which would have been likely to deliver the most snowfall at the resort, did not. It was the 1978-79 winter, a weak El Niño year, that brought the highest recorded snowfall in the data set of nearly 500 inches.
And it was a weak La Niña winter in 1974-75 that deposited the second-highest recorded seasonal snowfall of 463 inches.
Grover’s statistical analysis determined that snowfall during El Niño years was not significantly higher than the 55-year average, but that there was a statistically significant correlation between La Niña years and above-average snowfall.
“We're basically seeing the opposite of what El Niño and La Niña are predicting here, which is a pretty big deal,” Grover said.
Heidi Steltzer, a professor of environment and sustainability and biology, was one of the lead authors of the high mountains chapter in the 2019 Intergovernmental Panel on Climate Change report and has done extensive research on the impacts of climate change on snow and watersheds. The chapter concluded that as the climate warms, there is less snow in the mountains for shorter periods of time each year.
And, she said, Grover’s results are indicative of the mystery skiers face as the climate changes. Big snow years, such as this past one, are not entirely a thing of the past, nor do they indicate that climate change is not affecting snowpack.
“They’re sporadic, not predictable, so we should enjoy them while they’re here,” Steltzer said. “But we should not take a big snow year as an indication of a story we believe about the climate because belief in that story makes us feel safe.”
The project was made possible thanks to Robert McDaniel, 73, the founding director of the Animas Museum and retired head of Purgatory’s ski patrol. In the absence of an official custodian, McDaniel took it upon himself to collect, update and safeguard the records of Purgatory’s monthly snowfall dating back to 1965.
“Somebody had the wisdom to keep all the raw data sheets up there, but they were kept in a couple buildings that got demolished over time,” McDaniels said. “... I knew that when it came down to it and those places were going to get cleaned out and demolished, that stuff was going to get thrown away. So I grabbed it.”
But until Grover came along, the data and McDaniels’ efforts to maintain it had gone unappreciated. Steltzer said that McDaniel’s diligent record-keeping is an inspiration and indication of a growing conception that data collection is not just reserved for degree-holding academics.
“There's science being done all around us,” Steltzer said. “... If one historian in our community was able to do that (preserve this knowledge), there's many more people in our community that have done that. And there's the Indigenous tribes of our region that have been doing that and have been the knowledge-keepers – the folks who say ‘wait, let's not lose that piece of what we know’ – and that's what brings me hope.”
The data collected by patrollers and used in Grover’s analysis is different from the marketing snow totals splashed across the resort’s promotional emails.
This year, Purgatory Resort’s website reported a season total of 377 inches of snowfall – 40½ inches less than what was recorded by ski patrol.
The disparity is nothing nefarious, McDaniel says. It reflects the difference in how the numbers are collected. The snowfall totals advertised on the resort’s website are collected by the drivers of grooming machines at the end of the graveyard shift, while the numbers compiled by ski patrollers are collected later in the morning. The snow has time to settle as the sun crests the horizon, decreasing the apparent volume of snowfall over time.
Ski patrol also collects data at a consistent time and location. The information is provided to different agencies such as the Forest Service and the Colorado Avalanche Information Center.
But with Grover’s project complete, McDaniels’ work to steward that data over the years is no longer for naught.
“It’s great,” he said. “It really makes it worthwhile. It’s not just something I do for my own curiosity, it actually has some use to somebody in this world.”
rschafir@durangoherald.com
A previous version of this story gave incorrect years for the record snowfall at Purgatory Resort. The resort received the most snow during the 1978-79 season. The Herald was given incorrect information.
