WATERTOWN — Autumn and the equinox arrives at 9:03 p.m. Thursday in the region, and on its heels will be a climatological rarity.
For the third year in a row, we should expect to feel the effects of La Niña. The World Meteorological Organization says the three-peat would become this century’s first “triple-dip” La Niña, spanning three consecutive Northern Hemisphere winters (Southern Hemisphere summers).
“It’s pretty rare to have a third La Niña in a row,” said Jessica L. Spaccio, climatologist at Cornell University’s Northeast Regional Climate Center in Ithaca.
La Niña, translated from Spanish to “little girl,” is a natural ocean-atmospheric phenomenon marked by cooler-than-average sea surface temperatures across the central and eastern Pacific Ocean near the equator. It’s the opposite of El Niño (“little boy”) which features warmer-than-average sea surface temperatures in that region.
The cooler waters from La Niña affect the location of jet streams, which impacts North America.
“Right now, it has a high probability (91%) of continuing through the fall — September, October and November,” Ms. Spaccio said. “The probability goes down for January through March.”
The National Oceanic and Atmospheric Administration reports the chances of La Niña continuing decreases to 54% from January to March 2023.
La Niñas, Ms. Spaccio said, can have various effects, but other weather-making elements must be considered.
“Last year a moderate La Niña in Watertown in December there was kind of not much snow and kind of on the warm side,” she said. “But then in January, it was pretty snowy and cold. There are other things that come in play with our winters are large scale systems that are forecast on a short time period. We can’t forecast those until we’re a couple weeks out.”
And then there are pesky things like “arctic oscillation”: the back-and-forth shifting of atmospheric pressure between the Arctic and the mid-latitudes of the North Pacific and North Atlantic.
“Things like arctic oscillation can really shift our winter one way or another, and that can change throughout the winter as well,” Ms. Spaccio said.
During La Niña winters, the polar jet stream typically dips farther south. But no two La Niña or El Niño events are alike. A decade ago, in 2012, the north country was in the grips of a more substantial La Niña than what the past two years brought. When winter was over in March 2012, it had been one of the mildest and least-snowy seasons on record. It reached 77 degrees on March 19, 2012, according to Times files.
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