While we are still in an El Niño pattern as of April 2024, numerical model guidance shows strong signals of a changeover to La Niña this summer and into next winter. This article will explain what exactly La Niña is and what a La Niña episode could mean for summer weather and the 2024-2025 ski season.

Check out the current ENSO conditions of the sea surface temperature (SST) anomalies across the equatorial Pacific Ocean.

What is La Niña?

The term La Niña refers to the large-scale ocean-atmosphere climate phenomenon linked to periodic cooling in sea-surface temperatures (SSTs) 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 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) cooler 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 5 consecutive, overlapping 3-month periods.

Current La Niña Status

We are still experiencing El Niño conditions, but these are slowly weakening as of March and April 2024. There is now a La Niña Watch, because of the expected changeover by this summer around July-September 2024.

The transition to a neutral ENSO phase has already begun with an 85% chance we continue to transition from El Niño to ENSO-neutral by April-June 2024. The odds of La Niña developing by June-August 2024 is 60%. A look at the latest SSTs over the past year shows the slow trend of SSTs cooling, approaching average, and even below-average temperatures.

For reference, each Niño region is a different area along the equatorial Pacific Ocean. The Niño region most focused on for ENSO conditions is Niño-3.4.

These SST trends are expected to continue and SSTs will cool over the equatorial Pacific Ocean. The timeline of these expected changes in SST will mean:

• El Niño will persist through April-May 2024.
• Transition to ENSO-neutral during May-June 2024.
• Tansition to La Niña around July-September 2024.

Below is a look at the latest forecast of when the transition to ENSO-neutral and La Niña will begin.

Impacts of La Niña Summer

With the expected changeover to La Niña by July-September 2024, we can look at how La Niña can affect summer and fall weather across North America. The biggest effect La Niña causes is related to the hurricane season.

La Niña SST changes in the equatorial Pacific Ocean cause cool and dry weather. Cool and dry weather causes strong vertical wind shear in the Pacific Ocean. Wind shear is the rate at which wind changes speed and or direction in horizontal and or vertical directions. Strong wind shear is not good for hurricanes in the Pacific Ocean that affect Central America and California. 

In the Atlantic Ocean, there is the opposite effect of wind shear due to the cool and dry weather La Niña brings to the Pacific Ocean. There is more likely to be weak wind shear in the Atlantic Ocean, which can cause hurricanes to strengthen and become more frequent.

Every La Niña is different and unique, which can bring different impacts related to the hurricane season. Other weather patterns around the globe affect the hurricane season as well.

Impacts of La Niña Winter

We have been here before because we have seen La Niña winters from 2020-2023. There were three La Niña winters during this time and the last one during 2022-2023 gave the Western US record snowfall.

While it is too early to predict what this La Niña will bring for next winter, we can remind ourselves of what can happen (2022-2023) but also remember other winters that have not faired great in terms of snowfall for many areas in North America. Each La Niña is different and brings unique impacts.

Based on past winter weather patterns since 1950 during La Niña, we can reference what might occur during the 2024-2025 North American winter.

Impacts of La Niña on South America

La Niña brings cooler SSTs, which causes drier and cooler weather over the equatorial Pacific Ocean. This can cause drier weather on the western side of South America, specifically during the Andes Mountain ski season. While the research and patterns are not as clear for these areas, the 2020-2023 triple-dip La Niña caused a prolonged drought in many areas of South America.

Stay tuned to this article for your source on all things La Niña for the 2024 summer and into the 2024-2025 ski season!

Zach Butler