NOAA Makes it Official: La Niña Conditions Have Ended
Leaving a trail of drought, flooding, and possibly even record tornadoes in its wake, La Niña was finally declared dead today by the National Oceanic and Atmospheric Administration (NOAA). The declaration was based on the fact that ocean surface temperatures in the tropical Pacific Ocean have pretty much returned to normal. Ocean temperatures had been running about 2.5°F lower through much of fall and winter 2010. La Niña is characterized by an area of cooler than normal water in the tropical Pacific, as well as altered trade winds and rainfall patterns.
While the extreme weather makes consistent news headlines, La Niña itself doesn’t get as much time in the spotlight. But all weather takes shape within the broader landscape of climate. Or to use a boxing analogy, climate is the trainer, but weather throws the punches.
The tropical Pacific progressively cooled through the spring and summer of 2010, and the first advisory for the 2010-2011 La Niña was issued on Aug. 5, 2010. By January 2011, La Niña was helping usher in heavy rains and flooding in Queensland, Australia as well as flash floods and landslides north of Rio de Janeiro in Brazil. In Sri Lanka, ongoing rains and flooding displaced more than a quarter million people from their homes, and swamped much of the rice-growing region of the country.
La Niña events typically last approximately nine to 12 months. And this one was no different. However, some episodes, like the 1999 to 2001 event (dubbed by some scientists as the “La La Niña”) persist for as long as two years.
It’s important to keep in mind that all weather events are now also born into a warmer world. This long-term warming trend, also known as global warming, stacks the deck for more extreme weather events — which suggests that extreme weather could dominate the headlines for years to come.
It’s unclear how global warming is influencing natural climate cycles, such as La Niña and its sibling, El Niño. However, some studies do show shifts in these cycles that may be tied to climate change.
And La Niña is pretty robust and predictable in terms of the type of weather we expect due to its influence on the jet stream. On average, La Niña winters are warmer than normal in the Southeast and colder than normal in the Pacific Northwest. La Niña also features drier than normal conditions in the Southwest, Central Plains and Southeast. In contrast, the Pacific Northwest is more likely to be wetter than normal in the late fall and early winter. Judging by NOAA's maps of precipitation anomalies for fall 2010 and winter 2011, the signature of La Niña is pretty clear.