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La Niña Is Here and Expected to Continue Through Winter. Here's What That Could Mean for the United States. | The Weather Channel

The Weather Channel logoThe Weather Channel 9/10/2020 Linda Lam

La Niña has developed and is expected to last through the winter, which could impact the Atlantic hurricane season, as well as temperature and precipitation patterns in the United States over the next several months.

Below average sea-surface temperatures extend across the central and eastern equatorial Pacific Ocean. Atmospheric conditions also generally demonstrate that La Niña has developed, according to the latest outlook issued by NOAA on Thursday.

As a result, NOAA issued a La Niña advisory.

La Niña is the periodic cooling of the equatorial eastern and central Pacific ocean. When sea-surface temperatures are cooler than average by at least 0.9 degrees Fahrenheit (0.5 degrees Celsius), along with consistent atmospheric indications for at least three consecutive months, La Niña is considered to be present.

This is important because the interaction of this cooler-than-average water with the atmosphere can affect weather conditions thousands of miles away in the U.S. and around the world.

In addition, NOAA said there is a 75% chance La Niña will persist through the winter.

Most computer models agree, suggesting La Niña will last through at least February 2021. "The forecaster consensus supports that view and favors a borderline moderate event during the peak November-January season," NOAA said in its outlook.

La Niña and Hurricane Season

When La Niña is present, it can be a speed boost to the Atlantic hurricane season, but it is just one factor that can lead to an active year.

This is because the cooler waters of the Eastern Pacific Ocean cause less wind shear and weaker low-level winds in the Caribbean Sea. Less wind shear and weaker low-level winds are favorable conditions for tropical development.

La Niña can also enhance rising motion over the Atlantic Basin, making it easier for storms to develop.

This season has already been active, and there is still a long way to go. La Niña only raises the concern that the above-average activity may persist.

(MORE: It's the Peak of Atlantic Hurricane Season, But There's Still a Long Way to Go)

La Niña and Typical U.S. Winter Impacts

La Niña could have some impacts on temperature and precipitation patterns in the U.S. this winter. However, it is important to note that La Niña, El Niño or the lack of either, is just one piece of the atmospheric puzzle.

Nevertheless, there are some general themes frequently found in a La Niña winter in the Lower 48, according to NOAA:

-The southern U.S. experiences above-average temperatures and below-average precipitation.

-The northern U.S. experiences below-average temperatures (particularly the Northern Plains and Northwest) and above-average precipitation.

These themes develop due to the upper-level pattern often observed. The weather pattern that frequently takes shape includes an upper-level ridge of high pressure near the Aleutians, which pushes the jet stream northward over Alaska and then southward to near the U.S./Canada border. This keeps colder air across the northern tier. Additionally, the storm track is a bit farther north, leaving the South dry and warm.

The Weather Company’s primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.


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