Does this huge warm water blob herald an end to La Ni単a?

By Tom Yulsman | February 12, 2018 11:56 am
Is La Ni単a waning?

Departure from average of the surface and subsurface tropical Pacific sea temperature averaged over five-day periods starting in early January 2018. The vertical axis showsdepth below the surface in meters,and the horizontal axis is longitude, from the western to eastern tropical Pacific. This cross-section is right along the equator. (Source: ENSO Blog/Climate.gov figure from Climate Prediction Center data.)

La Ni単a is still with us and influencing drought and other weather patterns in the United States and elsewhere.

But check out the animation above. Thatlarge mass of warm water coursing through the depths of the Pacific Ocean may signal that by this spring, La Nadawill be with us.

The warm blob and other signshave prompted the Climate Prediction Center to peg the odds of La Ni単a fading to neutral conditions at 55 percent during the March through May season.

La Ni単a weather pattern

Here’s how La Ni単a tends to influence weather patterns across North America. (Source: NOAA)

La Ni単a part of the El Ni単o Southern Oscillation, or ENSO is characterizedbycooler than average surface water temperatures in a portion of the equatorial Pacific Ocean. Theatmosphere responds in ways that affect weather patterns far afield.

La Ni単aconditions took hold last fall, and they are still influencing our weather. That includesthe warm and dry conditions afflictingSouthern California, and thelow snowpack in much of Colorado, where I live.

SEE ALSO:Hot, Dry Conditions Take a Heavy Toll on Western U.S. Snowpack

But the warm blob seen in the animation abovesuggests that we’re on the cusp of change. Scientifically, it is known as a “downwelling Kelvin wave.”

ENSO expertEmily Becker says this mass of warm water has “chased away most of the cooler-than-average subsurface waters, leaving La Ni単a without its steady supply of cooler waters.”

Writing in a post on theexcellent ENSO Blog on the Climate.gov website, Becker elaborates:

This movement toward more neutral subsurface temperatures is one of the factors forecasters are looking at as we anticipate the decline of La Ni単a. Most of the computer models also foresee this transition, and overall, forecasters have come to the consensus of a 55% chance that La Ni単a conditions will dissipate by MarchMay, as the tropical Pacific transitions to neutral conditions.

Becker reports that La Ni単a’s impact on weather patterns has been consistent with what scientists would expect, especially the dry conditions across the southern half of the United States. (Unfortunately, even if La Ni単a does dissipate by spring, it will likely be too late to help Southern California.)

Althoughthe weather has responded in many places asexpected, it hasn’t done so everywhere.

Nowhere is that more evident than in southernAfrica, which ordinarily tends toward wetter conditions during a La Ni単a episode.But parts of the region are into year three of a devastating drought. It began during the particularly strong El Ni単o episode of 2015/2016. And unfortunately, La Ni単a does not seem to have dislodged the dry conditions.

You may have heard that Cape Town in South Africa is running out of water and has been heading for “Day Zero” in May when the taps are to be turned off due to dwindling water in the city’s main reservoir. The city actually received a big downpourlast Friday. But it is unlikely to make much difference.

Of course, La Ni単a and El Ni単o aren’t the only climatic phenomena that influence weather patterns. Californians saw this last winter, when the state received copious precipitation that refilled drought-stricken reservoirs. This was despite the fact that we werein the grip of the first dip in what expertscall a“double-dip” La Ni単a.

We’re in the second dip right now, and it’s stronger than the first. Yet contrary to expectations, southern Africa isdry.

In the end, with the climate system it’s all about odds, not absolutes. And sometimes, some regionsdefy the odds.

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ImaGeo

ImaGeo is a visual blog focusing on the intersection of imagery, imagination and Earth. It focuses on spectacular visuals related to the science of our planet, with an emphasis (although not an exclusive one) on the unfolding Anthropocene Epoch.

About Tom Yulsman

Tom Yulsman is Director of the Center for Environmental Journalism and a Professor of Journalism at the University of Colorado, Boulder. He also continues to work as a science and environmental journalist with more than 30 years of experience producing content for major publications. His work has appeared in the New York Times, Washington Post, Audubon, Climate Central, Columbia Journalism Review, Discover, Nieman Reports, and many other publications. He has held a variety of editorial positions over the years, including a stint as editor-in-chief of Earth magazine. Yulsman has written one book: Origins: the Quest for Our Cosmic Roots, published by the Institute of Physics in 2003.

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