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We're seeing a lot of headlines about El Nino, but what do they mean?

El Nino is coming: Epic event ahead?

Dr. Doug Gillham
Meteorologist, PhD

Saturday, May 3, 2014, 7:50 AM -

El Nino is coming!

We are seeing a surge in the number of headlines about the developing El Nino, with many proclaiming that this will be a "Super El Nino" or an "epic event".  

As we head into the summer, forecast confidence is high that an El Nino pattern is developing.  However, will this pattern really become as extreme as many are saying?

You may be asking, "What is El Nino, and why should I care?"  So, before looking ahead at the forecast, we will first take a look at some background information on El Nino.

EXPERT ANALYSIS: Dr. Doug Gilham appears on television as The Long Ranger and writes regularly for TheWeatherNetwork.com. His expertise can be read here


Typically, discussions of El Nino focus on Pacific Ocean water temperatures near the Equator, especially in the region just to the west of South America. During El Nino events we find warmer than average sea surface temperatures in this region. The image below is from the strong El Nino event of 1997-1998. The yellow & red colours highlight the warmer than average sea surface temperature that were found at that time to the west (left) of South America.  

This is in contrast to La Nina events which are associated with colder than average sea surface temperatures in the same region. The following map is from the 1999 La Nina.

Note the blue colours to the west of South America which represent colder than average sea surface temperatures in the same regions that were so warm during El Nino.


However, focusing on sea surface temperatures only tells us part of the story. 

These temperatures change in response to changes in the atmosphere above the ocean. Typically the air flow in this region of the world is from east to west (often referred to as the tropical easterlies or the trade winds). This persistent flow pushes the warmest surface water to the west and causes deeper and colder water to come to the surface (referred to as upwelling) near South America.

Fluctuations in the strength of these easterly winds will cause changes in the strength of the upwelling. When the easterlies weaken, there is less upwelling and sea surface temperatures are able to warm. When the easterlies increase in strength, the upwelling will be even stronger and sea surface temperatures will be even colder than average. 

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While the ocean water temperatures are affected by the flow of air in the atmosphere, changes in ocean water temperatures also  impact the atmosphere. Therefore, El Nino and La Nina events do have far reaching impacts on general weather patterns over other parts of the world, including Canada.


However, there is also a tendency to oversimplify the impact of El Nino on the weather. As a child growing up in Canada (and a lover of snow and snow days), I remember El Nino being blamed for both snowy winters and winters that had little snow.

The nature of the impact for a given region is highly variable depending on the strength of the El Nino and on whether we are at the start or end of an El Nino event. The impact also depends on whether the warm water is found primarily over the eastern Pacific close to South America or whether the region of warmest water is found further to the west over the central Pacific. 


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