The Return of La Nina

The Return of La Niña???!!!

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La Niña might return. The huge Pacific weather event that shaped last winter and this year’s miserable spring may come back.

SAY IT ISN’T SO! This could mean another frozen winter, continued drought in Texas and even a possibility of floods in the Midwest next spring. How likely is it? Should we be getting out the long winter underwear?

First—let’s do the world’s quickest review. A La Niña (Spanish for “little girl”) is the world’s strangest name for rotten weather. It is a huge pool of cool water in the tropical Pacific. The water cools the air above it – which changes air pressure—which changes wind patterns—which changes weather. Since the La Niña is huge, its impact affects global weather, including conditions in the US. (This combination of ocean and weather conditions is frequently abbreviated as ENSO).

This week the National Oceanic and Atmospheric Administration (NOAA), the agency that monitors weather, climate and ocean conditions, wrote: ENSO-neutral is expected to continue into the Northern Hemisphere fall 2011, with ENSO-neutral or La Niña equally likely thereafter. (Translation: Expect a normal fall and maybe winter will be normal and maybe it will be miserably cold.)

Yet the agency’s Climate Forecast System’s models writes: The CFS … predicts La Nina conditions to develop during the Northern Hemisphere fall 2011. (Translation: The La Niña and the crummy weather it brings will hit this fall and winter.)
CFS Forecast
The average of the US Climate Forecast System models predict the tropical Pacific will drop over 1°C (1.8°F) below normal, creating a cold La Niña. Source: NOAA

Huh? Which is it—normal weather or a cold La Niña?

Here’s what’s going on: Different nations are trying to predict whether La Niña will come back and they disagree. The US models almost all predict a cooler tropical Pacific. (See graph A) However the Korean models expect a mild warm El Niño. The French predict a neutral Pacific. Some of the Japanese models agree with the US that there will be a cool La Niña. It’s kind of a mess. When you average everything, all of the warm and cool models, the result is somewhere in the middle.
ENSO Model Predictions
Climate models from all over the world differ on whether or not there will be another La Niña and the average result is that the Pacific will remain normal. Source: NOAA

NOAA’s official pronouncement, is hedging between the global and its own CFS models. Unfortunately, the CFS has had a fairly good record for being right. So hope the global models are right and we have normal weather. Meanwhile, polish your skis in case snowy La Niña comes back!