El Niño and La Niña explained

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By Erin Jordan - bio | email | Facebook | Twitter

TUCSON, AZ (KOLD) - The sea surface temperatures of the equatorial East Pacific Ocean affect weather patterns across the world. 

With a shift from warm to cool back to warm sea surface temperatures about every three years, the influence on our weather can be very noticeable from year to year. 

During an El Niño, there are warmer than average East Pacific sea surface temperatures. 

La Niña is just the opposite with cooler than average East Pacific sea surface temperatures. 

The phase in between El Niño and La Niña is referred to as neutral with near average sea surface temperatures. 

The entire system is known as the El Niño/Southern Oscillation (ENSO). 

Here in the Southwest, the phase of ENSO can have a major affect on our weather year round. 

The following sceneries are not hard and fast rules, but general patterns observed over the many years ENSO has been studied by researchers across the globe. 

El Niño usually leads to a wet winter in Arizona, especially in January and February. 

But a fast developing El Niño during Monsoon 2009 was blamed for the low rainfall recorded across all of southern Arizona. 

El Niño weakens the monsoon winds needed to pump moisture into the state. 

La Niña generally means a good chance of monsoon rains adding up across the state during the monsoon. 

This phase of ENSO strengthens the moisture flow during the warm summer months, giving a better than average chance of rain in Arizona. 

On the flip-side, La Niña generally leads to a dry winter. 

ENSO is just one factor that goes into the monsoon and winter precipitation forecast. 

There are numerous other factors that affect precipitation from month to month and day to day.

All of these factors are taken into account when we release the forecast.

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