Ah yes, it's mid October, and many Minnesotans are biting their nails asking the age-old question: "what will the winter be like?" Even though, we all know, no one can truly predict our winters accurately.
You have have seen or will see, broad-brushed interpretations of implications for our winter based on another La Niña winter. Each season, I have to debunk these.
First of all, yes, we're officially in La Niña again, just like last winter and just like 3 of the past 4 winters.
And just like last year, this is a weak La Niña episode.
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A reminder, La Niña conditions are the opposite of El Niño. La Niña is observed when the equatorial waters off the west coast of South America are cooler than normal. El Niño is the opposite.
In very broad terms, La Niña generally means warm, dry conditions in the south, and wetter conditions in the Ohio River Valley region, southern/eastern Great Lakes, and the Pacific Northwest. We generally are on the edge of colder than normal conditions in Minnesota that stretch into western Canada and Alaska.
While there are very strong correlations between El Niño conditions and our winters - 8 out of 10 times are warmer than normal and less snow than normal - La Niña is much more mixed.
La Niña is expected to be weak again and may not even persist the whole winter. This means other factors can easily outweigh the La Niña setup in determining our prevalent winter conditions.
Below is a plot of various models showing the intensity of La Niña. The consensus is that we remain at about -0.5 deg C cooler than normal, a weak setup.
The highest probabilities of La Niña conditions last through midwinter, but by the January-February-March (JFM) period the odds are that we enter into "neutral" territory out of La Niña. It is worth noting, though it is far out, that we could be headed to El Niño territory for the following season ... but one winter at a time my dear friends.
I roll my eyes at the broad brushed predictions because they simply do not apply any longer. Our climate is changing so rapidly that climate change must factor equally if not more so than almost all other features.
I did an extensive analysis of La Niña and snowfall last year around this same time. You can read it here.
And what happened? We had 29 inches of snow in the Twin Cities, barely more than half of normal snowfall. We had near normal temperatures (at least when averaged out) but couldn't get frequent snowfall to save our lives. The story wasn't much better anywhere else in the state either.
In my analysis last year, and these NOAA maps show, we tend to have more snowfall in La Niña winters:
And, what was more encouraging, WEAK La Niña episodes yield MORE snowfall than stronger ones. My theory is that because we're not "too cold" to snow in a weak episode (i.e. if the signal is too strong, and we're frequently too cold, the good snowfall tracks stay well south of Minnesota).
I want you to note something in the maps above however. These analyses go back to 1959. What's changed from then until now? Oh, just winter. Winter temperatures have warmed a staggering +4.2 deg F in just the last 5 decades.
I know it's hard to visualize what a 4.2 degree shift looks like so here's some perspective. It's a shift in climate of about 175 miles. The Twin Cities basically now have the winter climate of Ames or Waterloo, Iowa of the past.
I grew up ski jumping because my father was in the 1976 Winter Olympics. A great measure, without using climate data, is by who still has ski jumps today because they have dependable mid-winter snow cover. I can tell you that Iowa does not.
The reality of today is that it's really hard to do winter analyses using data prior to the mid to late 1990s. Winters before then and after then are apples and oranges.
When we look at La Niña episodes since 1991 (which is the start of our current normal/average period of 1991-2020) we see a completely different winter perspective:
The average (mean) of weak La Niña winters is about 5 inches more snow than our normal of 52 inches in a winter season, but there's a HIGH degree of variability (+/- 24.5 inches of standard deviation). There's a notable decrease in snowfall in moderate years and then an uptick in stronger years.
Now of course, there are only 15 total La Niña episodes in that 24-year period, so it's a VERY small sample size, but it does line up anecdotally with what we've seen in recent years.
The basic takeaway as you stand back looking at this table is that there's almost no net difference in modern winters from any La Niña episode for Twin Cities snowfall. Winter temperatures are pretty similar.
Remember the triple dip La Niña, the three consecutive winters of 2020-21, 2021-22, and 2022-23, only one of those winter was slightly below normal and only one of those winters was snowy. The 2022-2023 winter was our snowiest on record, so that's noteworthy, but was it because of La Niña or something else?
In conclusion, the fact we're heading into a weak La Niña for winter is noteworthy but doesn't mean a whole lot. We have the blob of very warm Pacific waters and a developing polar vortex to watch along with with yet another warm year globally in 2025 (though not as warm as 2024).
I'll have more on a winter forecast in the coming weeks, but don't wax those skis just yet.