What is La Niña and how does it play a role in the Wisconsin winter outlook?

Beyond The Forecast

(WFRV) – Think of a huge construction project on the roads within your town. It re-routes traffic and causes some neighborhoods to be busier than others in your town. 

This is a perfect way to describe the impacts of La Niña and El Niño on the jet stream which influences our winter weather in the United States.  

The big construction project our comparison refers to is the water temperatures in the Pacific. Normally trade winds push warm water towards Asia.

In a La Niña phase, trade winds are stronger than usual which causes cooler water in the Eastern Pacific to surface. El Niño is the opposite and would have warmer waters in the Eastern Pacific if we were in that phase. 

This is one part of the ENSO cycle which is defined by opposing phases of warm and cool waters of the Pacific. The changes in water temperatures create a domino effect that changes the jet stream pattern in the U.S.

Notice how the average jet stream will tend to bring cooler air to our west, and wetter conditions close by. Wisconsin usually does not have a strong signal of winter impacts of La Niña compared to other areas in the United States. 

None the less the winter outlook from NOAA will call for those wetter conditions to slip into Wisconsin this year along with above-average temperatures.  

The phases of La Niña and El Niño usually last about 9 to 12 months. NOAA has given the current La Niña phase an 87% percent chance of lasting through the winter.

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