El Niño: What Does It Mean, What Is Its Global Impact And How Does It Impact Your Weather?

El Niño is an extremely important climatological phenomenon that drives weather not only for the U.S. but also the entire world.

This article breaks down the definition of El Niño, how it impacts the weather and why it matters.

Defining El Niño

Let's start with what it is not: El Niño is not a storm that can hit your community. It is a climate pattern, meaning it is not "weather", but it does affect weather.

To define El Niño, we have to start with the Pacific Ocean.

Under normal conditions, there are consistent winds moving from east to west along the equator. These winds are called trade winds.

As trade winds blow, they push warmer surface water westward towards Asia. Cooler water across the eastern Pacific near the Americas then rises to the surface in a process called upwelling.

During El Niño, these trade winds weaken, which allows for warmer water to begin to drift back to the Americas. El Niño begins when water temperatures are at least 0.5ºC above average in the eastern equatorial Pacific (or in the Niño 3.4 region, defined later).

El Niño often develops during the spring, then peaks during the fall and winter months, but this can vary. This climate phenomenon typically lasts less than one year.

American Impacts

Winter: El Niño causes substantial changes in U.S. winter weather by disrupting global atmospheric circulation, which alters the location and strength of jet streams.

The polar jet stream is one of the jet streams that drives weather across North America. A track further north means warmer and drier conditions for the northern U.S. and Canada and heavier rainfall and flooding for the South.

But again, this is a long-term pattern, not a day-to-day forecast. It may not look like this every day, but these are the predominant conditions during El Niño.

Spring: In the spring, we tend to see slightly more tornadoes during an El Niño across the West and the Southeast.

Hurricane Season: Here's one of the potential benefits of an El Niño... When El Niño conditions are present during hurricane season, there is an increased amount of wind shear in the Atlantic Ocean, meaning there is a greater difference in wind speed and direction between lower and upper layers of the atmosphere.

Hurricanes need consistency through the atmosphere for their centers to become organized enough for strengthening. Increased wind shear creates an environment that essentially caps hurricanes' strengthening and development, which can mean a less active hurricane season during El Niño.

It Is A Spectrum

While this article has been about El Niño, there's also a flipside to the equation.

You may have heard of ENSO's other major phase: La Niña.

La Niña happens when the trade winds are even stronger, which causes more upwelling, making it the cold cousin of El Niño. This change in water temperatures causes the polar jet stream over North America to shift further north, leading to warmer and drier conditions across the South while the North is wetter and colder.

In between El Niño and La Niña, we have what is called neutral conditions, which is when there is no significant above or below average temperatures across the surface of the Pacific Ocean.

Frequent Words You Hear And Their Definitions

Below is more of a popcorn section where I go through each of the main buzzwords you will hear when discussing El Niño. Some of these I defined earlier, but it doesn’t hurt to have a list of them all:

Upwelling: When cooler waters rise to the surface due to strong winds. The strength of trade winds determines how much water rises to the surface, which can massively impact weather for the U.S.

ENSO: The El Niño - Southern Oscillation. A recurring and natural climate fluctuation that features the relationship between trade winds and the sea surface temperatures in the eastern equatorial region of the Pacific. This term encompasses the entire spectrum from El Niño to La Niña and the Neutral phase in between.

Niño 3.4: One of the regions in the Pacific Ocean that climatologists monitor to determine the strength of ENSO. The sea surface temperatures in this region what determine the intensity.

Relative Oceanic Niño Index: The metric of how strong an El Niño is, using the Niño 3.4 region to see how far above or below the sea surface temperatures are compared to the surrounding sea surface temperatures.

Sea surface temperatures: How warm or cold the surface of the ocean is.

Teleconnections: the impacts of the ENSO on global weather such as drier or hotter weather.

El Niño Modoki: A separate phenomenon that occurs in the tropical Pacific Ocean. It drives its own weather, similar to a regular El Niño. This occurs when the warm water is located in the central Pacific rather than the eastern Pacific. An example is that California is wet during an El Niño Modoki. There is also a La Niña version where cooler water pools in the central Pacific.

Strong El Niño: when the trade winds decrease drastically as opposed to just slightly. The amount of warm water in the Eastern Pacific is generally what you are looking at. Typically defined as water temperatures 1.5 degrees Celsius warmer than average.

Normal/average: The standard often used when determining the El Niño/La Niña. This number is based on the most recent three decades of data.

Climate: The average of many years of weather, often a 30-year average.