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El Niño July update

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El Niño is in the forecast to develop this summer. The Climate Prediction Center (CPC), which tracks El Niño development, released the latest discussion on the forecast on July 10. According to the CPC, "the majority of models indicating El Niño onset within June-August and continuing into early 2015."During the monsoon in Arizona, El Niño tends to push towards a drier summer.

Evidence shows the ideal atmospheric set-up for the monsoon is weakened during El Niño summers. However, because of an active tropics in the East Pacific Ocean during El Niño summers, if that moisture makes it into Arizona then heavy downpours could add up rain totals very quickly. At the start of July this year, a surge of tropical moisture moved into Arizona, which increased storm chances across the state. As tropical moisture continued to flow into Arizona, some areas have already received impressive rain totals.

Click here for a look at how monsoon rain totals stack up against past El Niño summer

When El Niño coincides with the winter months, Arizona generally has a wetter than average winter. The winter storm track drops farther south than average allowing storms to dump more rain and snow on the state than is typical of an Arizona winter.

El Niño and La Niña refer to the sea surface temperature (SST) of the eastern equatorial Pacific Ocean, off the coast of central America. The temperature of the water in this area can influence weather across the world, including right here in Arizona. El Niño is when the SSTs are warmer than average versus La Niña, which is when SSTs are cooler than average. The below image from National Climate Data Center shows how El Niño influences weather during the cool and warm months in the Northern Hemisphere.  

The below image shows the latest El Niño forecast from the CPC. The '0.0' line indicates average SST. All the lines represent different computer models that forecast El Niño and La Niña. The thicker yellow line is the average of all the model data.  The letters at the bottom represent the months. For example, 'MJJ' represents May, June, and July. In the forecast, you can see that the yellow line is trending through summer and into fall. Once the line goes above '0.5', an El Niño is in the forecast. According to the models that could happen as early as June.

Earlier this year the developing El Niño looked similar to the start of the strong 1997/1998 event. However the numbers have since backed off and the CPC says "the chance of a strong El Niño is not favored in any of the ensemble averages for Niño-3.4. At this time, the forecasters anticipate El Niño will peak at weak-to-moderate strength during the late fall and early winter."  The below image is from Columbia University. The red bars show an increasing confidence that an El Niño will appear as we head through 2014.


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