Departure from normal of water temperatures in the Pacific Ocean on December 26, 2011 (left), and February 27, 2012 (right), show a rapid eroding of La Niña and the potential start of an El Niño pattern.
UPDATE 4 December: Probably not an El Niño for 2012/13 – read here for more. The American drought will probably continue, though.
A large change in ocean temperature patterns is underway in the equatorial waters of the eastern Pacific Ocean, as it appears La Niña – the colder than average water temperature phenomenon which has lingered in varying strengths for the past two years – is drawing to a close.
While offset in the eastern 2/3 of the North American continent by Atlantic-based atmospheric influences, the first year of La Niña helped contribute to an active, cold weather pattern across much of the United States. This winter the effects were more limited to the western coast of North America and especially Alaska, where snow pummeling by the foot have continued throughout the winter.
La Niña has also influenced the last two Atlantic hurricane seasons – providing more favorable wind conditions over the regions of the ocean where storms spin up, helping contribute to back-to-back 19-storm seasons, which was 97.9% above the 1950 – 2000 average of 9.6 storms per year. (Tropical storms becoming hurricanes was suppressed in 2011 by an unusual amount of dry air from Africa, in spite of favorable winds.)
La Niña has also helped keep global temperatures from setting monthly and yearly records, with a huge region of the Pacific kept with air temperatures a couple of degrees below normal to compensate for the lower water temperatures.
Typically the pendulum swings from one state to the other (though not necessarily with similar extremes) so as La Niña departs, conditions appear favorable for its much more well known counterpart - El Niño – to develop by year’s end. What will that mean, in general, for weather patterns over the next year?
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