The National Weather Service's Climate Prediction Center last week declared La Niña in full swing. Cooler-than-normal sea surface temperatures have been observed in the tropical Pacific and are expected to continue through at least the end of meteorological winter, which ends the last day of February.

These cooler conditions typically push the jet stream, the atmospheric highway that directs storms across the US, to the north over the western third of the country. With the jet bowing, or extending, to the north, the eastern part of the country will likely see a dip in the jet stream. And this "dip" is where many winter storms form.

The jet stream also behaves like a fence, keeping cooler, drier air to the north and warmer, more moisture-filled air to the south. The result? A more wavy jet stream over the Northeast increases the variability in the type of weather we experience here in New England.

Inconveniently for us, we'll see the jet stream meander north and south of the region, setting up periods of cold stretches followed by large temperature swings to warmer conditions. This will make forecasting the weather this winter a bit more challenging for us meteorologists.

The typical winter pattern of a La Niña brings a westward shift in above-average precipitation, leaving New England with closer to average amounts of snow and/or rain during the winter months.

There are a few key trends that are worth highlighting when it comes to La Niña and New England winters. And it is always helpful to look at previous seasons where a weak La Niña took place.

I hinted above that New England can expect more variability in the weather this winter, meaning more cold snaps with periods of warmer weather. The last two seasons where New England saw similar conditions were in 2024-25, just last year, and the winter of 2022-23.

Each of those two seasons saw slightly below-average temperatures, with precipitation totals almost exactly at the 30-year norm. Snow totals across New England were slightly higher than normal west of I-95, which is good news for snow lovers this year.

Another takeaway is that we can expect an increase in the number of storms, but a likely decrease in storm intensity. The caveat with an erratic jet stream? There's an increased chance of a significant nor'easter occuring if the localized weather patterns align.

Take a look, below, at the average snowfall across New England during a weak La Niña winter. Boston usually sees about average snowfall, with Northern New England trending with higher snowfall totals. Last winter, Boston saw over 2 feet of snow, or 28.1 inches.

We will continue to monitor how this La Niña takes shape as we get closer to December, but the confidence is high that La Niña will continue through January and possibly into February. Last winter's La Niña lasted until early April.

The return of La Niña could mean more erratic winter weather for New England - The Boston Globe