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La Niña is coming: what it means for winter in Pennsylvania

The National Oceanic and Atmospheric Administration predicts that La Niña will be joining us for the winter again and much of the US is expected to feel its effects.
Credit: WPMT FOX43
Dry and warm air for much of the south, cold and wet for the northwest.

PENNSYLVANIA, USA — Winter is just about six weeks away. Crazy, right? 

After a very mild October where we saw increased sunshine and warmer temperatures, Mother Nature is switching it up a little bit. 

The National Oceanic and Atmospheric Administration (NOAA) released the official winter outlook just over a few weeks ago, confirming that La Niña conditions are set to arrive starting in December. 

La Niña may sound daunting, but it's not a storm. Translated from Spanish for "little girl," La Niña is a climate pattern that ensues every few years impacting weather around the world.

During the winter months, La Niña normally brings below-average temperatures in the north and above-average temperatures in the south. 

But how does that work? 

Let's dive into the science of it. 

Credit: NOAA
Upwelling brings cold water to the surface, weakening the jetstream

As mentioned above, La Niña is not a storm in the slightest. It's simply a change in atmospheric conditions and it's all dictated in the Pacific Ocean. 

During normal conditions, trade winds blow from east to west, bringing warm water from South America to Asia. With La Niña it's a different story as trade winds are much stronger, pushing warmer water to Asia causing colder water toward the surface to replace it. This in turn shoves the jet stream northward.

So what does this mean for the Keystone state? Just to the west of Pennsylvania, there's likely to be more moisture, and just to the south is drier and warmer air. This ultimately means that the messaging is a little bit murky, but let's do a quick comparison. 

Last year in Pennsylvania was also a La Niña winter and brought above-average snowfall. Temperatures were also above average, meaning we could expect something very similar this year.

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