Following an epic 2022-2023 winter for the Western US that featured record snowfall in California and Utah, it's time to shift gears and take a look at the upcoming 2023-2024 season for the United States.

Winter outlooks contain an inherent degree of uncertainty since so many factors in the atmosphere are not predictable months or even weeks in advance. However, there are a few variables including ENSO (the El Niño Southern Oscillation) that can provide some clues.

El Niño Has Arrived

We are coming out of a streak of three consecutive La Niña winters – a rare occurrence that has now happened only three times since 1950.

During the spring months, the pattern quickly reversed from a La Niña phase into an El Niño phase. El Niño has continued to strengthen over the course of the summer and is a near certainty to remain in place through the winter of 2023-2024.

In fact, NOAA's latest model-based outlook projects a greater than 90% chance of El Niño persisting through the winter of 2023-2024.

Image: NOAA Forecast showing the probability of an El Niño, La Niña, and Neutral phase for each three-month period between the summer of 2022 and the spring of 2023. Red bars show the percent chance of an El Niño and the “DJF” label is for “December-January-February”.

What is El Niño?

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 eastern equatorial Pacific.

El Niño represents the warm phase of the ENSO cycle and means that the ocean water temperatures are warmer than average.

El Niño Criteria

1) The average sea surface temperatures in the Niño-3.4 region of the equatorial Pacific Ocean were at least 0.5°C (0.9°F) warmer than average in the preceding month.

2) The average anomaly of at least +0.5°C (+0.9°F) has persisted or is expected to persist for five consecutive, overlapping 3-month periods.

The current El Niño phase and the winter ahead

The relative strength of an El Niño is also an important factor when it comes to prevailing weather patterns. A given El Niño (or La Niña) phase is rated as weak, moderate, or strong depending on sea surface temperature anomalies.

Confidence is increasing that we could see a strong El Niño this year, which would officially occur if sea surface temperatures in the Niño-3.4 region of the equatorial Pacific Ocean are at least 1.5ºC warmer than average for three consecutive, overlapping 3-month periods.

The dynamical model average, indicated by the purple line below, is projecting this to happen in December-January-February.

Image: Plot of multiple climate models projecting the phase and strength of ENSO over time. Positive values of +0.5 or greater indicate El Nino, with values of +1.5 or greater over three consecutive 3-month periods indicate a strong El Nino. The dark purple line indicates the dynamical model average, and the “DJF” label is for “December-January-February”.

As of early August 2023, the sea surface temperature anomaly in the Niño-3.4 region has already increased to +1.1ºC with an additional upward trajectory expected through the fall.

Since 1950, there have been 8 winters in which a strong El Niño phase was present. The last strong El Niño occurred in 2015-2016.

The image below shows precipitation anomalies during these strong El Niño “analog” years.

Image: Departure from average precipitation from December through March during the strong El Nino analog winters of '15-16, '97-98, '91-92, '87-88, '82-83, '72-73, '65-66, and '57-58. Green areas show wetter (which usually means snowier) weather.

The next image shows temperature anomalies during strong El Niño years.

Image: Departure from average temperatures from December through March during the strong El Nino analog winters of '15-16, '97-98, '91-92, '87-88, '82-83, '72-73, '65-66, and '57-58. Green areas show colder than average temperatures and yellow/red areas show warmer than average temperatures. 

Far West

During strong El Niño phases, wetter conditions are favored across the Southwest and along the West Coast from California to the Pacific Northwest, including BC (not pictured). 

Across the Pacific Northwest and Western Canada, weak to moderate El Niños tip the odds in favor of drier winters with below-average snowfall. However, strong El Niños typically result in wetter conditions with little correlation between above or below-average snowfall. 

Further examination of mountainous regions with long-term snowfall records indicates that strong El Niños result in roughly equal chances of above or below-average snow seasons. In other words, stronger El Niños are usually better than weak or moderate El Ninos in this region.

However, temperatures are typically warmer than average across the Pacific Northwest during strong El Niños, which could indicate that average snow levels during storms are higher than usual. 

There is little correlation between snowfall and temperatures around Tahoe during strong El Niños, while the Southern Sierra Nevada Range including Mammoth, as well as the Southern California Mountains, have better odds of above-average snowfall.

Rockies

Strong El Niño winters favor warmer and drier winters relative to average across the Northern U.S. Rockies, and colder and snowier winters across the Southern Rockies of New Mexico, Arizona, and Southern Utah. 

Across the Central Rockies, there is less of a correlation. Drier winters are slightly favored across Northern Utah and Western Colorado, with little to no correlation near the Continental Divide in Colorado. 

East and Midwest

Across the East, wetter but also warmer than average conditions are favored on the eastern side of the Appalachians in the Mid-Atlantic with drier conditions on the western side of the Appalachians.

Northern New England as well as Wisconsin and Michigan have better odds of above-average precipitation during Strong El Niños as opposed to weak/moderate El Niños. However, temperatures are more likely to be warmer than average, which could indicate a higher percentage of rain vs. snow events. 

What About QBO?

In last year's winter preview, we briefly discussed the Quasi-biennial Oscillation (QBO) which describes trade wind patterns in the tropics.

There is some uncertainty with the QBO forecast but it is likely to be in either a neutral or an easterly phase this winter. Easterly phases have shown some correlation with drier winters across the West and cooler/wetter winters across the East. 

However, the sample size involving easterly QBO phases and El Nino phases (especially strong El Niño phases) is very small, so not much is known about how the interaction of these patterns influences North American winters.

Keep in mind that no matter how deep or light a winter is compared to average, when it comes to skiing it’s all about timing. Booking a trip 7-10 days in advance and for a general area that looks stormy will increase your chances of scoring deep powder days.

Finally, OpenSnow forecasters have published research on snowfall compared to similar El Niño events for Colorado, Utah, Tahoe, Jackson Hole, Oregon, Montana, Idaho, Washington, British Columbia, and Europe so be sure to check those out as well.

Alan Smith, Meteorologist