Fall in the Roaring Fork Valley is beautiful, with the changing leaves and exodus of tourists. It also marks the start of the countdown to the upcoming ski season — the reason many people relocate to the valley.
After three consecutive La Niña years, OpenSnow forecasters are growing confident that the upcoming winter will be an El Niño season.
“For the upcoming winter season, an El Niño looks to be in store, and better yet, current sea surface temperatures are showing a strengthening El Niño event,” Basalt-based OpenSnow meteorologist Sam Collentine wrote.
The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to periodic warming in sea-surface temperatures across the central and east-central equatorial Pacific. It represents the warm phase of the El Niño-Southern Oscillation (ENSO) cycle and means that the ocean water temperatures are warmer than average, according to OpenSnow. ENSO refers to the year-to-year variations in sea-surface temperatures, convective rainfall, surface air pressure, and atmospheric circulation that occur across the equatorial Pacific Ocean.
As of Aug. 10, the National Weather Service Climate Prediction Center predicts an El Niño to continue through the Northern Hemisphere winter, with greater than 95% chance from December 2023 through February 2024.
“Note that a strong El Niño does not necessarily equate to strong El Niño impacts locally, with the odds of related climate anomalies often lower than the chances of El Niño itself,” the prediction states.
While it’s tempting to jump to the conclusion that an El Niño year means more snowfall, Collentine said history shows that Aspen Snowmass tends to be right around normal for snowfall during El Niño events, with the potential for a stronger start and end to the season.
The last El Niño season was 2015-2016, which produced normal snowfall at Aspen Highlands, normal snowfall at Aspen Mountain, and slightly below-normal snowfall at Snowmass, Collentine wrote.
Collentine dug through data on snowfall in Aspen over the past 30 years and found the 30-year median snowfall is 166 inches. Looking at data from the past seven El Niño winters, the median snowfall during those El Niño years is 158 inches, or 95% compared to the 30-year normal. The past seven El Niño winters were 1982-1983, 1986-1987, 1991-1992, 1997-1998, 2002-2003, 2009-2010, and 2015-2016.
The past three years have followed a La Niña pattern, which is the inverse of an El Niño pattern, where the same ocean temperatures fall below-average, and is defined by wet, cold weather in the north and dryer, warmer weather in the south, Summit Daily reported.
However, neither pattern guarantees an outcome for winter conditions, especially at the local level.
“It’s one of the few things that we have any shred of ability to forecast six months in advance,” OpenSnow founder Joel Gratz told Summit Daily. “Just because there’s a correlation, it doesn’t mean that every year is guaranteed to be that way.”
According to Collentine, longer-range forecasts can identify possible storms 1-2 weeks (or longer) in advance; but often, forecast confidence in the details of each storm only begins to increase when the system is about one week away or closer.
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