Have you seen what AccuWeather's winter outlook says about Minnesota? As is always the case, every long-range forecast must be taken with a grain of salt because predicting the weather beyond a couple of weeks loses accuracy very fast.
That said, long-range forecasting from NOAA’s Climate Prediction Center has improved substantially in recent decades. Unlike the Farmer Almanacs and the winter outlook from AccuWeather, NOAA's long-range dart shows skill, meaning it’s better than a coin flip.
AccuWeather paints a vague picture for most of the country. In fact, the Twin Cities and Minnesota aren't singled out at all in the entire article. It’s much easier to give a vague forecast, like the almanacs, rather than a quantitative forecast, like NOAA.
What AccuWeather did do was discuss the potential impacts a "triple dip" La Nina, the polar vortex and the Tonga volcanic eruption could have on winter.
Triple dip La Nina will play a role
One of the big influencers on this year’s winter forecast, and AccuWeather agrees, will be the triple dip La Nina I discussed recently. This is a pretty rare event to have three consecutive winters of La Nina. It's only happened a handful of times so trying to garner any statistical predictability is impossible.
La Nina ever so slightly favors higher odds of cooler than normal conditions for Minnesota but mainly northwest through the Dakotas into western Canada. As far as precipitation goes, it’s pretty much a statistical wash.
If we look at our past two La Nina winters, 2020-2021 was warmer than normal and last year was slightly colder than normal, so the odds are that this year's winter temps being warmer or colder than usual is a coin flip.
When it comes to snow, the last two winters have been below normal, though not by much. 2018-2019 was our last big snowfall season, finishing more than two feet above normal in the Twin Cities thanks to five snowstorms in February that helped dump a record 39 inches in 28 days. We also had 10 inches of snow in April.
Snowfall is the most highly variable figure in our winters from month to month and year to year, and therefore the most difficult to predict.
AccuWeather appears to be forecasting above normal snowfall for northeast Minnesota and northern Wisconsin. Perhaps they’re banking on persistence forecasting. I’ve talked some about persistence forecasting, which is when you keep forecasting the same until the weather pattern changes.
One such persistence pattern that may pay off again this year is forecasting for early winter. There’s been a marked trend in recent years that our winters seem to get a late start with December being one of the fastest warming months in our climate record. Only four of the past 12 Decembers have been cooler than normal and half (6) were well above normal, so there’s definitely something to pay attention to there.
The polar vortex!
In recent years, the weather starting around mid-January has been very interesting. Something we’re learning more and more about is how the polar vortex is changing with climate change and how to better predict its behavior in winter.
There’s some research to suggest there are more disruptions as we lessen the temperature contrast between the arctic and mid-latitudes, but regardless, when the polar vortex is knocked off the pole, or significantly stretched, it unleashes unusual cold deep into midlatitudes across the north-central U.S., Europe or Asia.
This tends to happen late January through February, or in spring as the vortex begins its normal decline with increasing sunlight.
An odd topic the AccuWeather forecasters mention is the major volcanic eruption near Tonga earlier this year. While it’s true it unleashed a huge amount of water vapor deep into the stratosphere, it’s largely unknown what (if any) impact that has in the troposphere, where our weather occurs. It was a rare event without previous measurement and trying to decipher its impacts on winter weather is a wild card.
What we do know is when a large volcano blows a ton of ash, it has a cooling effect. The most recent example was the Mount Pinatubo eruption in the early 1990s, which had a measurable cooling impact on global temperatures for a couple of years.
The summer of 1993 is one of only two summers (along with 1902) that the Twin Cities failed to reach 90 degrees.
The Tonga volcano spewed extra water vapor into the atmosphere, which actually has a warming effect rather than cooling, so it's a giant mystery as to what that could mean for our winter weather.
The climate change elephant in the room
The big factor on overall temperature patterns is climate change. Forecasting ups and downs is easier when we look at the trends. Seventy percent of winters since 2000 have been warmer than the historical average. Of course, there are ups and downs in the overall trends.
One element of climate change is increasing snowfall.
A warmer atmosphere holds more water vapor and we are seeing more snow because of it, but much of it melts or comes at odd times, like April. And warmer than normal temps can lead to more rain or mixed precipitation instead of snow.
Your winter guess is almost as good as anyone's, especially this early. We’re just starting to see how the polar vortex will behave as October goes into November and our winter patterns are often taking shape pretty late into December in recent years.
For what it’s worth, the official NOAA forecast calls for better odds than not (40%) of below normal winter temperatures and equal chances of above or below normal precipitation.
This does line up with a more typical La Nina pattern. Time will tell, my friends. Either way, winter is coming.