On Monday, Ithaca received its first flurries of snow of the winter season — almost two weeks later than last year. Cornell experts explained that this delayed start could be an indicator of the season to come, with more precipitation falling as rain instead of snow reflecting broader changes in climate.
According to Prof. Art DeGaetano, earth and atmospheric sciences, director of the Northeast Regional Climate Center, Ithaca will be experiencing a La Niña winter as opposed to an El Niño winter.
In a La Niña winter, DeGaetano explained, the ocean in the Pacific is colder than usual, which affects wind patterns in the Northeast. These cooler ocean waters shift the jet stream — currents of air miles above the Earth — to the north.
El Niño and La Niña are both part of a cycle characterized by oceanic and atmospheric conditions, where the surface waters of the tropical Pacific Ocean warm or cool between 1 degree Celcius to 3 degrees Celsius, compared to normally every three to seven years. This natural climate oscillation can strongly influence weather all across the U.S. and other parts of the world.
“Typically, the northern tier of the United States will be colder than normal,” DeGaetano said. “But the other thing that happens during a La Niña winter, is that it tends to be wetter than normal, particularly across the Ohio Valley and western parts of New York.”
A wet winter could lead to more precipitation in general, said Sam Coplin ’22, a member of the Cornell Chapter of the American Meteorological Society.
“With [a La Niña] in the Northeast, we tend to have storms with more moisture, which may lead to a more active storm track in places like Ithaca,” Coplin said.
According to Coplin, the Ithaca region primarily receives lake-effect snow — precipitation generated by cold air blowing over warmer water in the lakes. This results in intense evaporation from the lake surface to form convective clouds, which cools the moisture, allowing it to fall back to the surface as snow. This effect is especially common in the Great Lakes region.
According to DeGaetano, La Niña winters typically have heavier snow to the east of Lake Ontario, a region that includes Ithaca.
But even this expectation of increased snowfall can’t offset the current effects of climate change.
“Even though La Niña might make it a little bit cooler than normal, the trend toward warmer temperatures that we’ve seen in winter will overpower that,” DeGaetano said. “We’ll probably end up on the warmer side of normal yet again.”
Prof. Angeline Pendergrass, earth and atmospheric sciences, anticipates this upward trend in temperature will continue.
“We expect to see more of the precipitation [this winter] falling as rain instead of snow, because we expect it to get warmer,” Pendergrass said.
According to Pendergrass, the change in average temperature in winter every year has been consistently higher than the change in average temperature in summer. In other words, winters are warming faster than summers.
And these effects of climate change have further implications for the Ithaca region, especially when considering the date of the first snow.
“If we look at the date that Ithaca normally sees its first inch of snow, that’s moved by a whole week,” DeGaetano said. “It used to be Nov. 20. And now with a new normal period, it’s the 25.”
Typically, a “normal” is the 30-year average of collected weather data in a particular region. Normals change every decade; the new normal ends with 2020 now that the year is completed. Before that, they ended in 2010.
With just 10 more years of data, the date Ithaca normally sees its first inch of snow has shifted by almost a week. DeGaetano anticipates this date may move out even further in the future as the climate continues to warm.
Cornellians may expect to be grabbing their shovels and their boots later and later as Ithaca winters become wetter, warmer and less snowy over time.
“We’re talking Ithaca specifically right now, but this pattern of changes matches a lot of what we see across the United States and across the globe,” DeGaetano said. “We’re not necessarily unique in those regards.”