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What the Impending La Nina Could Mean for the Winter

Jun 8, 2010; 5:38 PM ET

After going through moderate El Nino conditions this past winter, the El Nino Southern Oscillation (ENSO) has already transitioned back to neutral, and now it looks like we are quickly headed into La Nina territory for this summer and perhaps into the winter.

El Nino is the unusual warming of the equatorial Pacific surface waters, while La Nina is the unusual cooling of those same waters. Both can have major impacts on the world's weather, especially during the winter months.

The two maps below show the global sea surface temperature anomalies. The first map is from early January. Note the area of warmer anomalies stretching across the equatorial Pacific, which was indicative of El Nino conditions.

The second image is the most recent, and you can see that the same region is now showing mostly cooler-than-normal sea surface waters, indicating the trend toward La Nina.

You can also see the obvious trend away from El Nino and toward La Nina on the anomaly plots of the four Nino regions below......

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Here is the latest consensus ENSO forecast from several models, courtesy of IRI, that goes out into the winter. As you can see, a majority of models continue the trend toward weak La Nina conditions for the summer and into the winter (-0.5 or lower), while some others keep it close to normal.

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Let's assume that there will be either a weak or moderate La Nina for this upcoming winter. Climatology suggests that this winter will be very different from the winter of 2009-2010 over large portions of the country. Images below are courtesy of Environment Canada.

Weak La Nina temperature departures

Weak La Nina precipitation departures

Moderate La Nina temperature departures

Moderate La Nina precipitation departures

**Note: strong La Nina's typically bring well above-normal precipitation, including snowfall, to British Columbia and the Pacific Northwest.

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