We got the first measurable snowfall out of the way and this year, it came early. On average, we see the first measurable snowfall (defined by 0.1 inches or more) in the first week of November, this year it came about three weeks early which puts it in the top 10% of early snowfalls. It’s only the third time it’s been this early or earlier since the year 2000.
Whenever anything winter-like happens early, it begs the question among many; “what, if anything, does this mean about the upcoming winter??”
Most of the time we can safely say “absolutely nothing.” That’s because our four seasons are pretty different in Minnesota with very different atmospheric patterns. In recent years, our winter pattern doesn’t even establish itself until well into December, so deciphering anything out of an October event is silly.
But, let’s take a gander anyway shall we?
When we plot the date of the first snowfall versus the total seasonal snowfall that following winter we see, well, basically nothing as far as a correlation. The yellow dashed line is the average snowfall for the season (full historical record: about 47”):
There is a subtle trend in slightly higher amounts the earlier the first snowfall comes and the opposite is true later but it’s not strong. In an ideal world, we’d want to see all the dots line up as close to the trend line as possible and we’d call that a good ‘fit’ or correlation between date of the first snow and the total seasonal snowfall.
If we take a deeper dive and look at snowfalls that come particularly early, which I’ll define as those in the top 10% earliest (like this year), we see an even worse correlation, largely because there aren’t that many data points, only 14 years that have been around October 16 or earlier.
So, let’s take a look at temperatures. Do cold or mild winters follow an early or late first snowfall?
Again, it’s not a strong correlation at all, but the correlation is double that of comparing snowfalls. In general, there’s a subtle trend (which make sense) favoring slightly colder winters if your first snowfall comes early and a slight favorability for a milder overall average if it comes very late. However, once again, the data points are all over the place so it’s no slam dunk by any means.
If we dive deeper into the particularly early snowfalls (remember there are only 14 years, so it’s a statistically low sample size) there’s more of a trend:
BUT, there’s only a trend to colder winters if the first snowfall comes REALLY early, like late September or or the first week of October, not mid October (like this year).
So basically, this morning means just about nothing about the upcoming winter season either in terms of snowfall or winter average temperatures. BUT, if you’re curious, I ran the numbers to see what we come up with IF the winter were determined solely by the date of the first snowfall and it was an accurate correlation (neither of which are true so this if pure fun!):
Temperature: 18.2° (modern normal is 19.2°, historic average is 16.9°)
Seasonal snowfall: 51 inches (modern normal is 52.3”, historical average is 46.6”)
Make your winter plans accordingly! (Sarcasm!)
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