At a Glance

La Niña can affect snowfall patterns across the U.S.Weak La Niña events produce different effects than strong events.This winter features a weak La Niña.

Weak La Niña conditionsare officially in place and may , potentially influencing the weather conditions in the United States this winter,according to NOAA. This could include the amount of snow that falls over a given region.

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 0.5 degrees Celsius, along with consistent atmospheric indications, a La Niña is considered to be in place.

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La Niña, El Niñoor the lack of either, known as the neutral phase, is only one large-scale forcing on the atmosphere. It is not the sole factor in determining whether a season is wet, dry, cold or warm. Other atmospheric influences are in play, includingatmospheric blocking.

Nevertheless, there are some general themes to expect with regards to snowfall in aLa Niña winter, according to research by Dr. Stephen Baxter, a meteorologist with NOAA's Climate Prediction Center, published in a .

"Based on climate analysis ... we see that La Niña favors increased snowfall over the Northwest and northern Rockies, as well as in the upper Midwest Great Lakes region," Dr. Baxter said."Reduced snowfall is observed over parts of the central-southern Plains, Southwestand mid-Atlantic."

This is shownusing blue(above-average snowfall) and brown (below-average snowfall) shadings in the graphic below.

Snowfall departure from average for all La Niña winters (1950-2009), based on analysis at the Climate Prediction Center using Rutgers gridded snow data. Blue shading shows where snowfall is above average, and brown shows where snowfall is below average.

(Climate.gov/NOAA)

This is a common pattern during La Niña because the jet stream typically bulges northward over the North Pacific Ocean, resulting inmore blocking high-pressure systems that allow colder air to spill into western and central Canada and parts of the northern tier of the United States.

Meanwhile, storminess is often diminished in the southern U.S. as upper-level high pressure tends to lockin over the region. This causes the storm track to shift north into portions of the Ohio Valley and Great Lakes.

The graphic below demonstrates a general La Niña setup across the U.S. and Canada.

Typical impacts of La Niña on U.S. winter temperature and precipitation. Such impacts have been associated with past episodes, but all impacts aren't seen with every episode.

(Climate.gov/Fiona Martin/NOAA)

Weak vs. Strong La NiñaEvents

Dr. Baxter decided to dig even deeper into La Niña's correlation with snowfall by comparing weak La Niñaevents to strong La Niña events.

A weak La Niñais in place this winter, and the resulting weather could be different than if it were a strong La Niña.

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"In this preliminary analysis below, there is a suggestion that weaker events are snowier over the Northeast and northern and central Plains, on average," Dr. Baxter said.

Snowfall departure from average for weak La Niña winters (1950-2009), based on analysis at the Climate Prediction Center using Rutgers gridded snow data. Blue shading shows where snowfall is above average, and brown shows where snowfall is below average.

(Climate.gov/NOAA)

On the other hand, stronger La Niña events – shownbelow –are snowier across the Northwest, northern Rockies, western Canadaand the Alaska Panhandle, Dr. Baxter added.There is also a susceptibility toward below-average snowfall over the mid-Atlantic, New Englandand northern and central Plains, which is not seen during a weak La Niña.

Snowfall departure from average for strong La Niña winters (1950-2009), based on analysis at the Climate Prediction Center using Rutgers gridded snow data. Blue shading shows where snowfall is above average, and brown shows where snowfall is below average.

(Climate.gov/NOAA)

Overall, a strong La Niña has more of an effect on seasonal snowfall over western North America. Weak La Niña events often feature more widespread above-average snowfall across the northern tier of the U.S.

Keep in mind, however, other factors can override these typical patterns, so not every La Niña winter will follow these exact guidelines.

Brian Donegan is a digital meteorologist at weather.com. Follow him on,and .