El Nino No No: It’s Not a “Storm”, Though It Does Impact Weather

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I was browsing the internet the other day when this “gem” caught my eye:

I’ll admit, I like the boots… But this is a poor use of the term “El Nino”. I’m not surprised that a fashion blogger used the term for marketing purposes, but it is fundamentally incorrect.

El Nino is not a localized “storm” or “system” or a party that you would attend. Instead, El Nino is a teleconnection that spans a throughout the Pacific Ocean and impacts both ocean currents and global weather.

El Nino In A Nutshell

El Nino is simply the presence of abnormally warm ocean temperatures located along the equator in the Pacific Ocean. Below is an animation of the sea surface temperature anomalies from the past 12 weeks (September 23 through December 9, 2015) and is a classic example of El Nino.

These abnormally warm temperatures span from the coast of South America to as far west as the International Date Line, or 180°W.

Sea Surface Temperature Anomalies (Source: Climate Prediction Center)

Sea Surface Temperature Anomalies (Source: Climate Prediction Center)

Warmer than normal ocean waters definitely have an impact on the weather, though. An easy way to understand the impact is to consider a similar — but smaller — process that we experience in every day life.

NormalCirculations

Normal atmospheric and oceanic circulations. (Source: NOAA)

Imagine that you are starting a bath, and you have just turned on the water but not much has accumulated in the bathtub. The air in the bathroom is still relatively dry and cool, and you walk out of the bathroom for a moment.

When you go back in, you notice that not only has the bathtub filled with water, but the air in the bathroom is now warm and muggy. The bathwater has effectively warmed the air in the bathroom, and some of the water has also evaporated and is now present within the air in the form of humidity.

ElNinoCirculations

El Nino atmospheric and oceanic circulations. (Source: NOAA)

In a way, this experience illustrates the effect that El Nino has on global weather. The heat from the water transfers to the air above it, effectively changing the properties of the atmosphere above the ocean. Warm, moist air is less dense and so it rises, producing clouds and thunderstorms. The rising air and thunderstorms change the wind patterns downstream, and weather patterns become disrupted on a global scale.

Below is a schematic illustrating the typical impacts of El Nino on the United States. Most notable is that a southern branch of the jet stream, known as the subtropical jet stream, pumps moisture from the Pacific Ocean to the Southwest, including southern California, Arizona, and New Mexico. In addition, the subtropical jet stream brings additional moisture to the Southeast and often aids in the development of low pressure systems throughout the South.

typicalelninopattern

Typical impacts of El Nino on North American weather patterns. (Source: NOAA)

Also notice that during an El Nino, the polar jet stream is often shunted to Canada as opposed to making its traditional dip into the eastern third of the U.S. This allows traditionally frigid regions including the Midwest and the Northeast to experience much, MUCH warmer than normal winters.

With regards to the Tennessee Valley, the National Weather Service in Huntsville has published an extensive review as to how previous El Nino events have impacted weather in northern Alabama and southern Tennessee.

In addition, focusing on the “trend” during an El Nino does not mean that a winter will *always* be dry or wet or warm or frigid during the entire spanse of winter.

Bottom line, while it may be trendy to use phrases like “El Nino” for marketing purposes, it is really important to know what meteorological terms like this mean — otherwise you look foolish dressing for a party in the middle of the Pacific Ocean.

Now that I think of it, I *do* know the perfect outfit to wear to an El Nino…

– Christina Edwards

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