Last week the National Weather Service predicted a 75% chance for a La Niña winter in the northern hemisphere, anticipating the third La Niña year in a row.
“The probabilistic forecast for Southeast Alaska is a tilt towards another colder than normal winter,” said Rick Fritsch, forecaster at the National Weather Service in Juneau. “This is the third La Niña winter, which in itself is extraordinary and doesn’t usually happen.”
During La Niña, southern and interior Alaska are wetter and cooler than average, while the southern U.S. is warm and dry.
“What a La Niña means for us is a higher than normal probability for cooler temps,” Fritsch said. “However, cooler than normal can be a half a degree or 10 degrees. So when you look at the actual probability of below normal, this can mean a lot below normal or a little.”
Another driving factor for climate prediction is the Pacific Decadal Oscillation, or PDO.
According to data from the National Centers for Environmental Information, the PDO has been lower than -2 in recent weeks, meaning that sea surface temperatures in the Gulf of Alaska are significantly cooler.
“Last year was also a La Niña and a negative PDO. Those are basically our two signals for this upcoming winter,” said Erik Stevens, director and forecaster at the Haines Avalanche Center. “If the PDO stayed in a cold phase, that would also imply a cold year.”
Climate predictions based on El Niño predict average weather patterns over long periods of time, but long-term predictions have disadvantages.
“Generally, I don’t trust the forecast more than two days out,” Stevens said. “Our state of technology just isn’t there yet. The models they are using down south have a lot more accuracy because there’s more data, but up here in Alaska the models get pretty extreme beyond five days out.”
Importantly, our perception of winter can be changed by just one weather event.
“Really, it’s so variable, all it takes is one storm to change everything,” Stevens said. “Even on a cold, dry year, if we have one big storm in the middle of winter it will seem like a really snowy year.”
Overall, predictions based on La Niña are a matter of probability, not certainty. Haines residents should be prepared for any outcome.
“I wouldn’t wait; go get a snow rake just in case, look for air gaps in the house to cut down the heating bill, and pay attention to snow loading,” Fritsch said.
NOAA predicts La Niña to last from December 2022 to February 2023.
“Based on persistence, it’s likely to be the same as last winter,” Stevens said. “We are still in La Niña and still have a negative PDO. But that could have a lot of different effects in Haines. It could be wet, cold, dry; all these things are still completely possible.”