Latest forecast is less bullish on La Ni単a

By Tom Yulsman | July 14, 2016 1:04 pm

Even so, there’s still better than a 50/50chancethat this weather-influencing phenomenonwill emerge during fall and winter

La Ni単a

Sea surface temperature in June 2016 compared to the 1981-2010 average. The blue tones indicative of cooling in the central tropical Pacific suggest La Ni単a may develop later this year. (Source: NOAA Climate.gov map by Dan Pisut, based on GEO-Polar data.)

In the latest forecast, La Ni単a the coolopposite to El Ni単o is still favored to develop by winter. But the odds have dropped over the past month.

The U.S. Climate Prediction Center now pegs La Ni単a’s chances of developing at 55 to 60 percent. That’s down from odds of 75 percent just a month ago.

If it does develop, it is likely to be a relatively modest one, according to the CPC.

SEE ALSO: As El Ni単o fades, here comes La Ni単a

La Ni単a Impacts

La Ni単a’s typical impacts during December, January and February. (Source: Climate.gov)

Whether or not La Ni単a takes over from the now defunct El Ni単o of 2015 and 2016 is not just an academic question. These two sides of the El Ni単o-Southern Oscillation, or ENSO, have powerful effects on our weather. Click on the mapatright to see what the odds favor in terms of winter impacts, should La Ni単a developas predicted.

Whether or not La Ni単a takes hold could also influence California’s epic drought. That’s because La Ni単a tends to be associated with drying in California a trendthat can persist, and deepen, for years afterward.

SEE ALSO: If La Ni単a follows the current super El Ni単o, it will probably be bad news for drought-plagued California

During a La Ni単a, surface waters along the equator in the eastern and central Pacific Ocean tend to cool, the opposite of what happens during an El Ni単o. You can see hints of that cooling in the image at the top of this post.

Thisdrop in temperaturesis fed by a supply of cool water welling up from the depths. And right now, there is plenty of that available:

La Ni単a

This cross-section of the tropical Pacific ocean along the equator shows how water temperature down to a depth of 300 meters varied from average between July 5th and 9th 2016. The blue blob shows a massive volume of relatively cool water rising to the surface. (Source: Climate.gov)

The blue blob in the cross-sectionalgraphic above shows a massive volume of relatively cool water extending down to almost 250 meters in depth. It is just surfacing in the east (right), influencing surface waters there.

This is exactly what you’d expect with a La Ni単a. Sowhy isn’t the forecast a slam dunk for La Ni単a?

Anthony Barnston, chief forecaster with theInternational Research Institute for Climate and Society at Columbia University, has an excellent explanation over at the ENSO blog. So for a wealth of nitty gritty details, make sure to check out his post.

The long and short of it is this:The ocean seems to be talking, but the atmosphere doesn’t seem to be listening very well at least not yet.

For La Ni単a really to take hold, cooling of equatorial Pacific surface waters has to begin influencing what happens in the atmosphere above it. Typically, that means a strengthening of the trade winds that usuallyblowalong the equator from east to west.

In turn, that tends to enhanceupwelling of cool water from the depths in the eastern Pacific, which strengthens the trade winds even more, which causes even more cool upwelling all in a positive feedback loop that can push the whole system into an unambiguous La Ni単a.

Except right now, the trade winds haven’t seemed to notice what’s happening at the ocean surface below them. They’ve been blowing from east to west at about average strength.

The upshot: Conditionsdon’t look quite as conducive to La Ni単a as they did last month. But all of that could change once again especially if the trade winds wake up.

CATEGORIZED UNDER: Climate, ENSO, select, Top Posts, Weather
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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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