La Niña Watch for Northern Hemisphere: How this climate pattern could affect our upcoming winter

Weather Blog

ROCHESTER, NY (WROC) — We got our entertainment factor in on what our winter could hold with the annual Farmer’s Almanac winter outlook, but let’s take a step back and see what our friends at the Climate Prediction Center (CPC) are saying, using more of a climatological approach.

One week ago today on August 13th, the CPC issued a 60% chance of La Niña development with possible effects on the northern hemisphere during the fall and winter of 2020 – 2021. A watch is issued when conditions are favorable for the development of an El Niño or La Niña event within the next 6 months.

Image: CPC

First and foremost, what is La Niña?

It’s one of the two phases of the El Niño Southern Oscillation (ENSO) cycle. The other phase is called El Niño, which you may have heard more about. This recurring climate cycle creates the fluctuation in temperatures of both the central Equatorial Pacific ocean surface and atmosphere above it, where La Niña is considered the cold phase and El Niño is the warm phase.   

Photo: La Niña and El Niño from December 1997 & 1998 from weather.gov

During neutral conditions, trade winds that blow from east to west across the central Equatorial Pacific blow at a “normal” rate, but when these trade winds pick up in strength this results in the upwelling of colder water from deep within the ocean. Once this water rises to the surface it results in cooler than average sea surface temperatures to occur. This La Niña.   

Typically, El Niño and La Niña occur every 2-7 years with El Niño being more frequent, and each event can last from 9-12 months, even years at times. 

Here are the current conditions of the Equatorial Pacific courtesy of the CPC:

The red colors indicate warmer sea surface temperature (SST) anomalies, and the blue indicates cooler anomalies. You can see the hint of La Niña especially in the top image as more of the cooler ocean waters are beginning to make their way westward.

Why does this grab our attention? Simply because these changes in the ocean temperatures can have much larger scale impacts on our weather and climate across the globe. Specifically, when this pattern changes it usually has noticeable effects on us here in the northeast. What do I mean by that? 

Image courtesy: pmel.noaa.gov

During La Niña, the cooler ocean temperatures displace the jet stream northward creating warm and dry conditions for those across the southern United States, with warm and wet conditions occurring across the northeast. 

I know you’re all probably wondering the same thing, does this mean we’ll get more snow? Less snow? A combination of both snow and rain? More ice events? It’s not easy to say considering we also have our Great Lake as an influence to contend with, and we all know how lake effect snow can have a mind of its own.

Below are snow anomalies from samples based on 20 previous La Niña events dating back to 1950:

Photo courtesy: weather.gov

This only goes to show that it’s not always black & white in determining the outcome.

Here’s what the CPC is saying in terms of temperature and precipitation anomalies for November, December, and January:

Photo courtesy: CPC

They’re calling for a good chance of above average temperatures across the 3 month period, and little idea on what precipitation will look like. Even though it’s difficult and near impossible to determine what our winter will look like, we often look to climate patterns such as this to help guide us and get an idea on what could unfold.

Does this mean you should gear up now? Not really. Could this mean we do in fact have a warmer and wetter winter? Maybe, but there are so many factors that go into what type of winter we end up seeing.

So yes, the farmer’s almanac also mentioned the warm and wet winter, but now we can look at the current climate conditions and become more confident in what could potentially happen.

With that in mind our friends at the CPC and even the Farmer’s Almanac are more than likely using the forecasted ENSO conditions to make some of their assumptions, and although it’s still unsure exactly how our winter will end up playing out when it comes to specifics it will only become more clear as we get closer to the winter months. 

~Meteorologist Christine Gregory

Copyright 2020 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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