For the upcoming 2024-2025 winter season, La Niña conditions are growing and are favored to emerge during the late fall.

Before getting into the details on what that could mean for Jackson Hole and Grand Targhee, it's important to remember that any winter outlook will contain an inherent degree of uncertainty.

Long-range forecasts are rarely accurate. These forecasts cover 3-6 months but we know that skiing quality improves and degrades with storm cycles that last a few days to a week.

La Niña, Explained

The term La Niña refers to the large-scale ocean-atmosphere climate phenomenon linked to periodic cooling in sea-surface temperatures across the central and east-central equatorial Pacific.

La Niña represents the cool phase of the ENSO cycle and means that the ocean water temperatures are cooler than average.

La Niña Forecast for the Winter of 2024-2025

"ENSO Neutral" conditions (neither La Niña nor El Niño) have persisted through the summer of 2024 and long-range models have been projecting a higher-than-average chance of a La Niña taking over during the winter of 2024-2025.

Image: NOAA Forecast showing the probability of an El Niño, La Niña, and Neutral phase for each three-month period between the summer of 2024 and the spring of 2025. Red bars show the percent chance of an El Niño and the “DJF” label is for “December-January-February”.

The weekly Nino-3.4 region index (sea surface temperatures in the east-central Pacific) anomaly has dropped from 1.8°C during the 2023-2024 winter season to -0.1°C as of September 9, 2024.

Long-range models are projecting this to be a weak La Niña episode with sea surface temperatures ranging from -0.5 to -1.0ºC in the east-central Pacific. 

A similar change from El Niño to a weak La Niña last occurred ahead of the 2016-2017 winter season.

We have identified six winters since 1990 in which weak La Niña conditions were present:

• 2000-2001
• 2005-2006
• 2008-2009
• 2016-2017
• 2017-2018
• 2022-2023

We will use these winter seasons that featured a weak La Niña as “analog” years for this analysis.

Historical Weak La Niña Seasons @ Jackson Hole & Grand Targhee

After looking back at the six weak La Niña winters and comparing them against the 30-year median of total snowfall through March 31 of 390 inches for the Rendezvous Bowl Plot at Jackson Hole Mountain Resort (elevation 9,580 feet), I've found that the median snowfall during those years is 459 inches or 118% compared to the 30-year normal.

• 1991-2020: 390" (30-year normal)
• 2000-2001: 302" (77%)
• 2005-2006: 453" (116%)
• 2008-2009: 465" (119%)
• 2016-2017: 560" (144%)
• 2017-2018: 452" (116%)
• 2022-2023: 561" (144%)

Five out of the six weak La Niña years produced well above-normal snowfall, and only one produced well below-normal snowfall.

For timing, when looking at the median monthly snowfall during those six weak La Niña winters and comparing them against the 30-year median snowfall for each month:

• October: 33" (102%)
• November: 60" (109%)
• December: 106" (135%)
• January: 88" (106%)
• February: 84" (125%)
• March: 84" (125%)

There is a strong signal for abundant early-season snowfall in December, with five of the six analog years featuring above-average snowfall, while above-average snowfall is also favored from January through March.

Note: The period of record for snowfall at Grand Targhee is too short to evaluate for this study with records only dating back to 2008, but year-to-year and month-to-month variations in snowfall tend to be very consistent at Jackson Hole vs. Grand Targhee since they are located in the same mountain range. 

Temperatures During Weak La Niña Seasons

While snowfall is what we pay attention to the most during ski season, temperatures are also a factor in terms of snow quality.

For temperatures, I examined the Moran weather station next to Jackson Lake, which has the most complete temperature data in the area. I compared winter seasonal and individual monthly temperatures during the 6 most recent weak La Niña winters to the 30-year averages. 

For the four-month winter period from December to March (which corresponds to lift-served ski season), I found that temperatures are 1.6ºF colder than average during weak La Niña winters.

When examining individual monthly temperatures from October through April during the six weak La Niña winters compared to the 30-year averages:

• October: 38.6ºF (-0.1º)
• November: 24.7ºF (-0.7º)
• December: 13.8ºF (-1.3º)
• January: 12.3ºF (-1.3º)
• February: 16.1ºF (-1.3º)
• March: 23.5ºF (-2.6º)
• April: 33.5ºF (-1.1º)

While near-average temperatures are favored prior to ski season in October, below-average temperatures are favored from November through April.

This signal tells us that, for the season as a whole, snow quality could potentially be lower-density and more powdery compared to a normal winter – though this will vary from day to day and storm to storm as always. 

2016-2017 Winter Season

As mentioned above, the Niño-3.4 region index anomaly as of September 9, 2024, is down to -0.1°C, which is similar to where it was ahead of a La Niña event during the summer of 2016.

Since this last occurred back in 2016, let's have a little fun by looking back at the snowfall during the 2016-2017 season in the Tetons. Some of you may remember the infamous power outage storm in Teton Village during February of that season.

2016-2017 Snowfall through March 31:

• 560" - Jackson Hole (Rendezvous Bowl)
• 501" - Jackson Hole (Raymer Plot)
• 431" - Grand Targhee (Chief Joseph Bowl)
• 415" - Jackson Hole (Mid-Mountain)
• 230" - Snow King
• 212" - Jackson Lake
• 160" - Jackson Hole (Base Area)
• 110" - Town of Jackson

* Data courtesy of Bridger-Teton Avalanche Center

Overall, history tells us that snowfall at Jackson Hole and Grand Targhee tends to be above normal during weak La Niña winters, and temperatures tend to be colder than normal.

Having said all of this, for skiers and snowboarders, keep in mind that when it comes to finding the best conditions, it’s all about timing. To have the best chance of enjoying the deepest powder, our recommendation is to dial in your plans 7-10 days in advance.

Sometimes, 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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Alan Smith