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Bad news for Arizona, La Niña to return?

Published: Jul. 8, 2011 at 12:44 AM MST|Updated: Jul. 15, 2011 at 10:57 PM MST
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During a La Niña event, cooler-than-normal water pools off the west coast of South America.  This results in less evaporation of the ocean water and in turn less precipitation in southern Arizona during the winter.  Now, it appears possible that La Niña may return this autumn, just in time to severely limit winter precipitation.

Last winter, the winter of 2010-2011, southern Arizona was parched.  La Niña was largely responsible for the lack of precipitation.  During the period December, 2010 - March, 2011, the Tucson International Airport, the official reporting station for Tucson, recorded just 1.19" of rainfall, leaving a rainfall deficit of 4.40".   The 1.19" of rainfall equates to just  20% of the normally expected rainfall for the same period.

In a forecast issued in early July by the Climate Prediction Center, a branch of the National Oceanic and Atmospheric Administration, climate scientists hinted at the possibility of a returning La Niña during Autumn, 2011.  Although the majority of computer models indicate a continuation of neutral (not El Niño or La Niña, but "normal") conditions, the report says that "forecasts have begun to indicate the re-emergence of La Niña during northern hemisphere fall 2011."  The following image shows those forecasts.  Note the lines curving BELOW the X-Axis toward the right side of the graphs.  The right side is Fall and Winter 2011-2012.  These plots indicate cooler-than-normal conditions in the Pacific, ala La Niña.

A return to La Niña conditions in the fall of 2011 could reproduce the drought and ensuing disastrous wildfire season that Arizona experienced in the winter of 2010-2011 and the following spring.