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 Idaho, 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 snow 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.

Ski Season Snowfall vs. La Niña

The map below shows winter snowfall during seven La Niña episodes. The lower the number, the stronger the La Niña. The blue dots are above average, the white dots are average, and the orange dots are below average snowfall.

"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.

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.

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

Thanks to my colleague Alan Smith, 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.

Based on snowfall from our analog years most of the state will be about average for the upcoming season. When we analyzed the analog years for mild La Ninas we found that the following areas were within a few percent of the median:

Bogus Basin: 100%

Brundage: 99%

Lookout: 99.6%

Schweitzer: 102%

What is interesting is that there are a few areas that seem to be favored during a mild La Nina winter:

Galena Summit: 120%

Pomerelle: 113%

Soldier Mountain: 128%

Other Resources:

WeatherBell:

I like to also take a look at WeatherBell to see what their general forecast is for the upcoming winter. They have generally done a good job in years past. Obviously, they are not as specific as our analog forecast is, but it is nice to see a trend for our region.

Luke Stone:

I like to keep track of what Luke thinks as well. He has done some incredible research relating the Atlantic QuadPole Mode to the ENSO forecast and deriving a precipitation forecast from that. The long and short of his research predictions is in the graphic below where green indicates above-average precipitation and brown indicates below-average precipitation. 

For a more in-depth explanation click HERE.

Conclusion:

I like our chances of an average snowfall year.

There are some areas that seem to be favored in a mild La Nina (the central mountains) and most of the state should be near or even slightly above average by the time the season ends. The best way to guarantee good powder is by being flexible and paying attention to the daily/weekly forecast using OpenSnow. Good powder days can even be found in the worst snow years.

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