NewsOctober 4, 2012

Forecasts Call for Weak-to-Nonexistent El Nino This Winter

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Andrew Freedman

By Andrew Freedman

Despite earlier hype, this winter may not be an El Niño winter after all, meaning that California may not be plagued by intense storms, but also that the Southwest may not see badly needed drought relief. Because El Nino affects North American weather patterns, forecasters closely watch its development. Lately, the picture has become more muddled.

According to the Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI), El Niño conditions have not yet fully emerged in the tropical Pacific Ocean, and the odds that an El Niño event, which could lead to a stormy West Coast and southern tier of the country this winter, will develop later this fall or winter are just 50-55 percent, down from 70 percent one month ago.

Precipitation departures from average during El Niño years from 1950 to 2010.
Click on the image for a larger version. Credit: NOAA.

El Niño events, which are part of a broader natural climate cycle known as the El Niño/Southern Oscillation, or ENSO, occur about every 3 to 7 years on average. In order for El Niño to form, a delicate dance needs to take place between the ocean and the atmosphere in the form of a series of feedbacks. Such feedbacks include a slackening of the trade winds that blow from South America toward Southeast Asia, and they end up reinforcing the above-average sea surface temperatures. However, so far, the ocean and atmosphere have not worked in tandem, making El Niño’s development less likely.

El Niño events often have ripple effects (referred to by climate forecasters as “teleconnections”) throughout the atmosphere and oceans, altering weather in North America, South Asia, Australia, and even Africa.

In the U.S., El Niño winters often bring above-average precipitation to the West Coast (except for Oregon and Washington), above-average temperatures to the Pacific Northwest, and can feature an active jet stream that steers storms across the southern tier of the country. California, in particular, can experience severe winter storms during El Niño winters, while the Southwest, which is suffering from long-term drought conditions, can see above-average precipitation as well.

As recently as September, climate forecasters were anticipating that an El Niño event would take shape in the Pacific, and that a weak-to-moderate El Niño would be present during the 2012-13 winter.

However, during the past few weeks, sea surface temperatures cooled slightly in the equatorial tropical Pacific, and weather patterns have failed to exhibit clear signs of a developing El Niño. In an ENSO update released Thursday, climate forecasters said the atmosphere and ocean are in a “borderline” neutral-to-weak El Niño state.

“Due to the recent slowdown in the development of El Niño, it is not clear whether a fully coupled El Nino will emerge,” CPC and IRI forecasters said in an update posted online.

Tony Barnston, chief forecaster at IRI, cautioned against counting El Niño out just yet.

“At present we consider that we have a borderline El Niño, meaning the atmosphere, and now lately also the sea surface temperature anomalies, are not clearly in the weak El Nino range, but only approach the threshold of that range,” he said in an email conversation.

Sea surface temperature departures from average as of October 4, 2012. There is an area of warmer than average water in the eastern equatorial Pacific, but it is not warm enough to be classified as El Niño conditions.
Credit: NOAA.

“Our official outlook is for about a 50-55 percent chance for a weak El Niño still developing during the coming month or two, lasting through the remainder of 2012. This outlook indicates that we still think El Niño is possible, despite some others' statements of a 'fizzled' event.”

Barnston said that it can be harder to predict how a weak El Niño will influence winter weather patterns compared to a moderate or strong El Niño. “Teleconnections are less well defined for weak than for strong events. Besides possibly/probably (but not necessarily) being weaker, a more frequent result is that some of them do not appear at all, while some of the others do,” Barnston said.

In other words, there may be even more uncertainty about the winter weather outlooks that are going to be released later this month, as forecasters consider how much of a role a borderline El Niño may play.

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