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 of what that could mean for Oregon, 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.

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.

Historical Weak La Niña Seasons @ Mount Hood Resorts

After looking back at the six weak La Niña winters and comparing them against the 30-year median snow water equivalent (SWE) on March 31 of 53.3 inches at the nearby Mt Hood Test Site SNOTEL station, I've found that the median SWE during those years is 53.1 inches on March 31 or ~100% compared to the 30-year normal.

SWE on March 31 During La Niña

• 1991-2020: 53.3" (30-year normal)
• 2000-2001: 35.9" (67%)
• 2005-2006: 63.8" (120%)
• 2008-2009: 63.1" (118%)
• 2016-2017: 53.9" (101%)
• 2017-2018: 42.8" (80%)
• 2022-2023: 52.3" (98%)

Two out of the six La Niña years produced well above-normal snowfall, two produced near-normal snowfall, and two produced well below-normal snowfall.

For timing, when looking at the change in SWE each month during those years and comparing them against the 30-year median change in SWE for that month:

• November: 7.6 (106%)
• December: 11.5 (95%)
• January: 7.9 (77%)
• February: 10.3 (118%)
• March: 11.3 (117%)

This gives us a signal that the start of the season starts normal and turns below-normal, before a strong finish with an above-normal finish to winter.

Historical Weak La Niña Seasons @ Mt. Bachelor

After looking back at the six weak La Niña winters and comparing them against the 30-year median snow water equivalent (SWE) on March 31 of 35.9 inches at the Mckenzie SNOTEL station near Bachelor, I've found that the median SWE during those years is 37.2 inches on March 31 or ~104% compared to the 30-year normal.

SWE on March 31 During La Niña

• 1991-2020: 35.9" (30-year normal)
• 2000-2001: 22.0" (61%)
• 2005-2006: 51.9" (145%)
• 2008-2009: 57.3" (160%)
• 2016-2017: 40.1" (112%)
• 2017-2018: 27.8" (77%)
• 2022-2023: 34.2" (95%)

Three out of the six La Niña years produced well above-normal snowfall, one produced near-normal snowfall, and two produced well below-normal snowfall.

For timing, when looking at the change in SWE each month during those years and comparing them against the 30-year median change in SWE for that month:

• November: 5.3 (100%)
• December: 9.7 (96%)
• January: 6.6 (89%)
• February: 8.4 (114%)
• March: 5.6 (139%)

This gives us a signal that the start of the season starts normal and turns below-normal, before a strong finish with an above-normal finish to winter.

Historical Weak La Niña Seasons @ Hoodoo

After looking back at the six weak La Niña winters and comparing them against the 30-year median snow water equivalent (SWE) on March 31 of 27.2 inches at the nearby Hogg Pass SNOTEL station, I've found that the median SWE during those years is 23.5 inches on March 31 or 86% compared to the 30-year normal.

SWE on March 31 During La Niña

• 1991-2020: 23.5" (30-year normal)
• 2000-2001: 21.0" (77%)
• 2005-2006: 39.5" (145%)
• 2008-2009: 27.7" (102%)
• 2016-2017: 25.4" (94%)
• 2017-2018: 13.5 (50%)
• 2022-2023: 21.5 (79%)

One out of the six La Niña years produced well above-normal snowfall, two produced near-normal snowfall, and three produced well below-normal snowfall.

For timing, when looking at the change in SWE each month during those years and comparing them against the 30-year median change in SWE for that month:

• November: 3.9 (101%)
• December: 7.6 (96%)
• January: 5.1 (91%)
• February: 3.9 (91%)
• March: 4.2 (90%)

This gives us a signal that the start of the season starts normal and we stay just below normal through the heart and end of the season.

Historical Weak La Niña Seasons @ Mt. Ashland

After looking back at the six weak La Niña winters and comparing them against the 30-year median snow water equivalent (SWE) on March 31 of 26.8 inches at the Big Red Mountain SNOTEL station near Mt. Ashland. I've found that the median SWE during those years is 27.2 inches on March 31 or 102% compared to the 30-year normal.

SWE on March 31 During La Niña

• 1991-2020: 26.8" (30-year normal)
• 2000-2001: 11.3" (42%)
• 2005-2006: 37.9" (141%)
• 2008-2009: 21.0" (78%)
• 2016-2017: 37.4" (140%)
• 2017-2018: 11.3" (42%)
• 2022-2023: 33.4" (125%)

Three out of the six La Niña years produced well above-normal snowfall and three produced well below-normal snowfall.

For timing, when looking at the change in SWE each month during those years and comparing them against the 30-year median change in SWE for that month:

• November: 2.1 (95%)
• December: 5.9 (107%)
• January: 5.0 (97%)
• February: 4.8 (114%)
• March: 4.4 (100%)

This gives us a signal that the winter season is right around normal or slightly below normal for snowfall.

Historical Weak La Niña Seasons @ Ski Anthony Lakes

After looking back at the six weak La Niña winters and comparing them against the 30-year median snow water equivalent (SWE) on March 31 of 15.4 inches at the Wolf Creek SNOTEL station near Ski Anthony Lakes, I've found that the median SWE during those years is 16.4 inches on March 31 or 107% compared to the 30-year normal.

SWE on March 31 During La Niña

• 1991-2020: 15.4" (30-year normal)
• 2000-2001: 11.0 (71%)
• 2005-2006: 20.9 (136%)
• 2008-2009: 17.4 (113%)
• 2016-2017: 15.4 (100%)
• 2017-2018: 10.9 (71%)
• 2022-2023: 17.8 (116%)

Three out of the six La Niña years produced well above-normal snowfall, one produced normal snowfall, and two produced well below-normal snowfall.

For timing, when looking at the change in SWE each month during those years and comparing them against the 30-year median change in SWE for that month:

• November: 2.1 (93%)
• December: 4.5 (113%)
• January: 4.0 (96%)
• February: 1.8 (70%)
• March: 3.4 (179%)

This also gives us a signal that the start of the season starts normal to above-normal with a dip to below-normal in February, but a strong finish in March at the end of the season.

Temperatures During Weak La Niña Winters

While snowfall is what we pay attention to the most during ski season, temperatures are also a factor in terms of snow quality. It is especially important in Oregon where snow levels can be a significant factor in the winter season. 

I examined NOAA’s, National Center for Environmental Information (NECI) Climate Division dataset, which takes in station observations throughout the United States. A quick look at the NOAA/NECI map below for the La Niña winters analyzed above shows below-normal temperatures for all of Oregon from November through April.

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 Oregon.

Data courtesy of BestSnow.net:

• Mt. Hood Meadows: 556" (125%)
• Mt. Bachelor: 538" (124%)

Overall, history tells us that Oregon tends to see variable snowfall during weak La Niña winters, with a slight favorability for above-normal snowfall.

• This variability comes from a few below-normal snowfall and a few above-normal snowfall winters during the six similar weak La Niña episodes.
• Winters tend to start normal, turn below normal, and then have a strong above-normal snowfall finish in March.

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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Zach Butler