It was a top question on Monday: “is it normal to have rain in January!?” The answer? It is now, yes. In the new and ever changing world of climate change people often refer to things now as the ‘new normal.’ This is a confusing term because when people say it they mean this is what happens now but shouldn’t. In meteorological and climatological terms, normal and average have set definitions. Normal refers to an average over a set time period and average would be the average of the whole data set. For example, in the Twin Cities, we have a reliable temperature record that goes back to 1873. If I tell you the January average temperature is 13.6 degrees, that’s every January averaged together over the full 149 year record. If I tell you the January normal average temperature is 15.9 degrees, that’s the current/modern normal we use that averages Januarys from 1991 through 2020. We use that set for our ‘normal’ until 2030.
Of course capturing an average when things are changing as fast as they are is complicated and requires some in depth analysis. It has rained in January in the Twin Cities and Minnesota before of course, but not at the frequency we now see. We picked up about 0.54 inches of precipitation Monday into Monday night, of that, about 0.34 inches was plain old liquid rainfall. It’s our second rainfall event this month. Last week the rain was in the form of freezing rain. Most of these totals you see below were in the form of rain across southern Minnesota:
At the same time, Iowa had very rare January tornadoes. There were four tornado reports in eastern Iowa. They were the first tornadoes reported in Iowa in January in 56 years:
Of course Minnesota had its first ever December tornadoes last year (2021) and let’s hope it’s a while before we see them in January, though yesterday’s storms were just about 90 miles south of the Minnesota/Iowa border.
Back to rain, in Minnesota, in January. We know average January temperatures have warmed dramatically, about 5 degrees over the historical record. That’s more than three quarters of a standard deviation, and we’ve talked about this before: when you move the average, you exponentially increase the probability of extreme events. January rain, can indeed be considered a pretty extreme event when we look at the big picture.
It is now about 2 to 3 times more likely to experience rain in January than it used to be. Through most of our historical record, we’d have a January rainfall event about every other year on average. Now? We average 1 to 2 events *EACH* January. The number of rainfall events in January since 2010 has never been experienced in our pile of records.
The average probability a century ago of a January rainfall was just under 2% and now it’s nearly 5%, still not terribly common, but as mentioned it’s now a fairly normal annual occurrence, if not more than once.
Januarys are indisputably much warmer, wetter with more frequent events that used to be much more rare. It’s certainly quite a bit different than when my late grandparents were born in 1919 and 1920.
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