We recently posted the 2023-2024 Winter Forecast Preview which discussed the role that El Niño will play on temperature and precipitation for the upcoming winter in North America. 

To recap, El Niño means that water temperatures in the Central Pacific Ocean are warmer than average, and this change in water temperatures can change weather patterns around the world. Here in North America, El Niño often creates wetter/snowier conditions along the southern part of the United States with drier conditions for the Northern Rockies and parts of the Ohio Valley.

While El Niño (warmer ocean water temperatures in the Central Pacific Ocean) and La Niña (colder ocean water temperatures in the Central Pacific Ocean) have been studied for decades, there are fewer studies about how ocean water temperatures in the Atlantic Ocean impact wintertime rain and snow across North America.

The quick summary of the research that I will present below is that due to warm ocean water temperatures in the North Atlantic Ocean during the summer of 2023, the 2023-2024 winter could be wetter (more rain and snow) for some areas compared to what we would normally expect if we only looked at El Niño in the Pacific Ocean and did not factor in ocean temperatures in the Atlantic Ocean.

What is the Atlantic Quadpole Mode?

The focus of my graduate research was how ocean water temperatures in the North Atlantic alter the typical impacts of El Niño and La Niña. 

Just like the warming and cooling waters of the tropical Pacific Ocean, the water temperatures in the North Atlantic Ocean cycle between warmer and colder as well, and we call this cycle the Atlantic Quadpole Mode (AQM). 

The warm phase of the ocean water temperatures in the North Atlantic, known as the warm AQM, is shown below.

The image above shows the warm AQM pattern with warmer-than-average ocean water temperatures across the northern Atlantic Ocean shown in red colors.

Why do Atlantic Ocean water temperatures matter for seasonal snowfall forecasts?

When a part of the northern Atlantic Ocean is warmer (or cooler) than average, it changes the circulation of the air above the Atlantic Ocean, and this changes the balance of atmospheric pressure in the region. 

This change in air pressure around the Atlantic Ocean then changes weather patterns in other parts of the world.

In other words, the effects of the changes that happen in the Atlantic Ocean do not stay in the Atlantic Ocean but rather spread across the globe. This is similar to how El Niño and La Niña, which are changes that happen in the Pacific Ocean, spread their effects around the world.

Based on research from past seasons, we know that ocean water temperatures in the North Atlantic alter the alignment and strength of the correlation between El Niño and La Niña and winter precipitation in North America.

Using ocean water temperatures in the North Atlantic, we can:

1. Provide more predictability about winter precipitation in areas of the United States that are not too far north and not too far south. This middle area is where there is a low correlation between El Niño, La Niña, and the amount of rain or snow.
2. Enhance our ability to forecast in all areas of the United States as we now have two predictors: Ocean temperatures in the Pacific and ocean temperatures in the Atlantic.

Below are the typical precipitation patterns associated with La Niña and El Niño during winter. Green shows areas of above-average rain and snow while brown shows areas of below-average rain and snow.

If we only look at La Niña and El Niño, then we are left with these two maps, and cannot say much about times when La Niña or El Niño is weak or non-existent (called “Neutral” conditions).

However, we now have more information as we can look at La Niña, El Niño, AND the status of ocean water temperatures in the Atlantic Ocean.

Making a forecast using both Pacific and Atlantic water temperatures

For a winter season with both El Niño and a warm AQM, that is, warmer-than-average ocean water temperatures in the Central Pacific and the North Atlantic, we see wetter/snowier conditions push farther north throughout the western United States. Look at panel “C” below.

For a winter season with both El Niño and a cold AQM, that is, warmer-than-average ocean water temperatures in the Central Pacific and colder-than-average ocean water temperatures in the North Atlantic, we see fewer wetter/snowier areas within the Western United States. Look at panel “A” below.

For a winter season with both La Niña and a cold AQM, that is, colder-than-average ocean water temperatures in the Central Pacific and the North Atlantic, we see fewer wetter/snowier areas within the United States. Look at panel “G” below.

For a winter season with La Niña, and a warm AQM, wetter/snowier areas extended farther south (panel “I” vs “H” below), yet a cold AQM increases the extent and magnitude of areas with below-average precipitation (panel “G” vs. “H”).

The image above shows precipitation patterns associated with Pacific Ocean water temperatures (La Niña, neutral, El Niño) and Atlantic Ocean water temperatures (Cold AQM, Neutral AQM, Warm AQM). Green shows areas of above-average rain and snow while brown shows areas of below-average rain and snow.

The winter 2023/2024 outlook using BOTH ENSO and AQM

Forecasting the ocean water temperatures in the North Atlantic months in advance of winter is more difficult than forecasting ocean water temperatures in the tropical Pacific Ocean.

However, if the warm North Atlantic Ocean water temperatures that we are seeing now continue into the winter, then we will expect both El Niño in the Pacific Ocean and a warm AQM in the Atlantic Ocean. The global SST anomalies for the last three months are shown below. 

The image above shows ocean water temperatures over the last three months compared to average. The red/yellow areas are warmer than average while the blue colors are cooler than average.

Looking back at past winter seasons with BOTH a warm Central Pacific Ocean (El Nino) and a warm North Atlantic Ocean (warm AQM) results in the following precipitation pattern.

The image above shows precipitation patterns associated with an El Niño and a Warm AQM, which is what we expect for the 2023-2024 winter. Green shows areas of above-average rain and snow while brown shows areas of below-average rain and snow.

If El Niño and a warm AQM continue into winter, and if past correlations continue, then we expect above-average precipitation in the Southwest and all of California, along with Southern Utah, Southwestern Colorado, and the Front Range of Colorado.

Lastly, it is important to remember that both the El Niño and warm AQM precipitation patterns shown here are an average of many years, and any individual year may depart from these averages. Further, it is possible that ocean water temperatures in the North Atlantic could change between now (late summer) and the beginning of winter.

Thank you for reading this winter snowfall outlook based on my research into North Atlantic ocean water temperatures and their impact on wintertime precipitation patterns across the United States.

Luke Stone
Forecaster, OpenSnow