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 Northern CA/NV, it's important to remember that any winter outlook will contain an inherent degree of uncertainty.

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.

With the help of 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.

Historical Weak La Niña Seasons @ Central Sierra Snow Lab

The Central Sierra Snow Lab is a staffed weather lab located just to the NW of Lake Tahoe near Donner Summit, almost directly across the road from Sugar Bowl ski area, and they take their measurements near 7000 ft (6894') in elevation.

After looking back at the six weak La Niña winters and comparing them against the 30-year median snow water equivalent (SWE) on April 1st of 33.4 inches at the Central Sierra Snow Lab, I've found that the median SWE during those years is 40.2 inches on April 1st or 120% compared to the 30-year median.

SWE on April 1st During a Weak La Niña

• 1991-2020: 33.4" (30-year median)
• 2000-2001: 13.7" (41%)
• 2005-2006: 45.6" (137%)
• 2008-2009: 34.8" (104%)
• 2016-2017: 66.9" (200%)
• 2017-2018: 20.2" (60%)
• 2022-2023: 74.9" (224%)

2 out of the 6 La Niña years produced well above-average snowfall, 2 produced near-average snowfall, and 2 produced well below-average snowfall.

For timing, when looking at the snowfall each month during those years and comparing that against the 30-year median snowfall for that month we get this:

• October: 4" (114%)
• November: 20" (75%)
• December: 36" (67%)
• January: 76" (117%)
• February: 124" (181%)
• March: 115" (232%)

This gives us a signal that the first half of the season could be below-average, while the 2nd half could be above-average for snowfall.

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 winter season for Northern CA/NV, in and just to the south of the Tahoe basin.

Data courtesy of my obsessive recording of daily reported snowfall:

• Palisades: 728"
• Northstar: 708"
• Sugar Bowl: 783"
• Boreal: 751"
• Homewood: 588"
• Mt. Rose: 761"
• Diamond Peak: 494"
• Sierra at Tahoe: 620"
• Heavenly: 659"
• Kirkwood: 685"
• Dodge Ridge: 504"
• Bear Valley: 481"

You'll want to take this with a grain of salt because this was a massive season for both total precipitation and snowfall, and no one is crazy enough to forecast that this far in advance, but it is in the analog list for this season. But so are well below-average seasons.

2016-17 saw higher snowfall to the north and less as you went south through the Sierra, which is typical to see more snow in the Pacific NW and farther north in CA during a La Nina season. We also saw a lot of atmospheric river storms that season, with a lot of rain as well.

Overall, history tells us that Northern CA/NV on average tends to be near normal to slightly above-average for snowfall during weak La Niña winters.

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.

Upgrade to OpenSnow All-Access for 10-day snow forecasts, expert local analysis, and custom snow alerts to help you find the deepest snow and the best ski conditions all winter long.

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Stay tuned...BA