A wet, stormy late fall and December lingers into January so far
It’s been quite the winter so far and it all really began in November when we went from an incredibly dry pattern to now a very soggy one. The other switch was from a pattern of warmer than normal conditions for 7 consecutive months (May through November) to a chillier one in December. December averaged just over 3 degrees colder than normal for a change.
We’re experiencing our third snowiest season to date behind only the infamous 1991-1992 season, which got a running start from the Halloween blizzard and then a stormy November overall and then the number two spot, the winter of 1983-1984, which would go on to be the snowiest winter ever recorded at 98.6 inches! If we make it to the 1983-1984 status, that means we’re only half way there folks!
You’ll note (above) that the 1991-1992 season was almost flat-lined in December, it’s still #1 at this point in the season because the Halloween Blizzard and the end of November storm that year really piled up the snow early on.
Of course snowfall is one thing about snow is made of water and so looking at the overall liquid equivalent trends can yield some interesting (and overlapping) information. While we don’t quite know the precipitation to date ranking yet, it’s certainly in the top 5.
Snowfall and precipitation can vary a lot because normally in mid winter in Minnesota our ratio of snow to water is higher than the often touted average of 10:1. Not so in this recent storm. For the first round, the ratio was about 9:1 with a very high water content. Compare that to our storm before Christmas where the ratio was a little more than 17:1.
We saw 1.29 inches of liquid equivalent precipitation in this recent storm, that is a HUGE amount of moisture for a January snowstorm. It’s in fact the third largest precipitation event in January history. The average total January precipitation is just 0.88 inches. This is because generally, January snowfalls are colder with those higher ratios, so 0.88 inches of water can easily equal a foot or more of snow.
We can talk more about January as the month goes on and finishes up and we’ll see if this stormy pattern persists but for now December is an interesting month to look at as far as long term trends are concerned. And essentially, even this storm is a left over of the pattern that has been going on since November and December.
Decembers are getting MUCH warmer over time, in fact, while January is our fastest warming winter month when you look ‘big picture,’ in recent years, December is outpacing January. So this December was unusual for recent trends in that it was 3.3 degrees cooler than normal but it was actually about what the historic average was. The reason this matters, is that a warmer atmosphere holds more water vapor and while it was chilly just in our region for one month, the overall atmosphere was warmer and super-charged with moisture which at least partly is contributing to our high precipitation/snowfall.
When we look at December precipitation since 1873 in the Twin Cities, we see an undeniable increase in precipitation. The green line is the overall trend line and the red line is the 10 year moving average. We can see that most recent decade or two have been the wettest Decembers on record overall.
If we look further at just the past 5 decades, since 1970, we see an even more dramatic trend. In fact, December is averaging nearly double the amount of precipitation now as 50 years ago. Looking at the temperatures above we can draw the conclusion that Decembers are getting A LOT warmer and A LOT wetter.
Even in Minnesota’s rapidly warming winters, it’s still cold enough, most of the time for precipitation to fall more as snow than as rain (though mid winter rain events are on the increase)… at least for now.
Will this pace keep up all winter? That would be unlikely if history’s a guide but of course there are outliers like the winter of 1983-1984. What I think happens in January will be discussed in a ‘coming soon’ post.
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