While a 'super' El Niño looks to be off the table, what does develop this year might not deliver what many Canadians are hoping for

Monday, July 28, 2014, 5:00 PM - As predicted earlier in the year, any chance for a 'super El Niño' to develop this winter has faded over time, and the latest word is that the pattern seems to be settling onto a course towards a weak El Niño by year's end. However, what's developing in the equatorial Pacific Ocean now is not exactly what forecasters typically see in this kind of situation, and it could result in some very interesting and unexpected weather in the coming seasons.

Earlier in the year, with the first mention of the potential for an El Niño developing later this year, some predicted that this could be a very strong El Niño, like was seen in 1997-1998. Phrases like 'super El Niño' and even epic El Niño were seen in the news. The evidence wasn't particularly strong for this type of scenario in the first place and it has been getting weaker since. Now, while the signs of an El Niño are still there - with between a 70-80 per cent chance of it developing later this year - it appears as though the chances of a strong El Niño are off the table.

The reason for this is a somewhat unusual situation we're seeing in and over the Pacific Ocean. To understand that, let's first take a look at what normally goes on with the El Niño Southern Oscillation (ENSO).

El Niño and La Niña - the two 'halves' of ENSO - are caused by changes in how the atmosphere and ocean in the equatorial Pacific behave. Under normal or 'neutral' conditions, the surface of the ocean is much warmer in the west, near Indonesia and northeastern Australia, and cooler in the east, near Peru and Ecuador. Along with this, the atmosphere has a long 'conveyor belt' circulation that spans the entire breadth of the Pacific, with air rising over Indonesia and sinking near South America. Under 'El Niño' conditions, the warmer sea-surface temperatures shift eastward, so that it is warmer off the coast of Peru and Ecuador and in the central Pacific, while the atmosphere circulation weakens overall, and shifts so that there is rising air over both Indonesia and the central Pacific, with sinking air in the east. The figures shown to the left (credited to NOAA and David Stroud) demonstrate these patterns well. When the normal pattern is pushed to an extreme, so that there are unusually cold conditions in the central Pacific, these are considered La Niña conditions.

What's going on this year, at least so far, is that the ocean surface temperatures are behaving roughly the way they should for a developing El Niño. Temperatures are warming up in the eastern and central regions of the equatorial Pacific. Specifically, the temperatures in the central Pacific (what forecasters call the Niño-3.4 region) have been about half a degree above normal, which is one of the criteria for declaring that El Niño conditions are present (but not that the El Niño is in full-swing). That's only one condition, though. Since the atmosphere plays a big part in this, it has to follow suit with the ocean temperatures, or the whole thing breaks down. So far, the atmosphere is still behaving like it does under neutral conditions.

According to Emily Becker, of Climate.gov, "the wind patterns are roughly average over the tropical Pacific, with some slight weakening of the trade winds toward the end of the month."

"There is increased convection in the central Pacific, but also some over Indonesia," she added, "all of which says we’re still waiting for the atmosphere to get dressed in its El Niño clothes and come out to play."

NEXT PAGE: What could this mean for the winter to come?

Even with the atmosphere still getting its act together over the Pacific, there is still a very good chance that we'll see El Niño conditions develop in the months to come, and have a weak El Niño in full swing by the end of the year.

When word spreads of an El Niño in the works, it's tempting to take this as a promise of a warmer, drier winter, which some would certainly welcome after the bitter cold endured this past winter, but the pattern developing in the equatorial Pacific right now is a little unusual, and it might not deliver on that promise. There are other factors to consider when trying to tell exactly what an El Niño will bring with it (it's never simple is it?), but one of the complications comes from within El Niño itself. Since ocean temperatures rise in two different parts of the ocean due to an El Niño, having one region with higher temperatures than the other changes the outcome.

When there is more warming in the eastern part of the ocean, it results in a more 'classic' El Niño. This pattern is a juggernaut, overwhelming nearly all of the contributions from the other patterns and oscillations that normally have an influence on North American weather. While it holds sway, this type typically results in the generally warmer, drier winter that many Canadians tend to expect from an El Niño. However, when there is more warming in the central Pacific, this produces what's known as an El Niño Modoki - 'modoki' being a Japanese word roughly equivalent to 'almost, but not quite' in English. So, whereas the classic El Niño 'juggernaut' tends to stand alone, the El Niño Modoki is just one 'player' on the field, allowing the other patterns and oscillations to have a greater influence on the weather. The overall effect of this is that, in those El Niño Modoki events, it's harder to know what to expect.

As of this month, forecast models appear to be pointing in that direction again, as the December-January-February forecast from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) shows:

Credit: JAMSTEC

Indeed, according to University of British Columbia climate scientist Simon Donner, all of the El Niño events seen since the 1997/98 event have been of this 'almost, but not quite' kind. 

Notably, 2002-2003 was considered a moderate El Niño Modoki, featuring warm temperatures across B.C. and the prairies during the first few months of 2003, while the eastern half of the country dealt with its longest and coldest winter of the 20 years previous. There were also exceptional events like Atlantic Canada's most expensive rainstorm, and a once-in-a-century ice storm in New Brunswick. The weak El Niño Modoki in 2004-2005 brought a 'Tropical Punch' of warm weather to B.C., while the Prairies were suffering through blizzards and deep freezes and the Maritimes were being buried in snow. In Ontario, the winter seemed like it would never end. Conversely, for 2009-2010 - another moderate El Niño Modoki episode - the warming climate, along with the influences of the Arctic and North Atlantic Oscillations, were all able to exert their influence over that season, producing The Winter that Never Was for many Canadians. However, had the other oscillations pointed in another direction, the situation could have turned out far differently.

What's likely to happen this year? Well, as with the examples above, it's really not easy to tell. Numerous agencies and researchers around the world are monitoring the temperature conditions in the equatorial Pacific and providing regular updates (click here for a look at Environment Canada's latest sea surface temperature anomalies), while we here at The Weather Network are keeping a close eye on the situation as well. Stay tuned to our forecasts and news stories for more updates to come.

(H/T to Dr. Doug Gillham for his invaluable contribution)