Remember St. Paddy’s Day 2012? You know, that 80-degree one? The only one ever in the Twin Cities? What also made it memorable is that the actual March 17 holiday fell on a Saturday.
On second thought, it’s remarkable people remember since there were probably more than a few hangovers given that combo of summer warmth and the right spot on the calendar.
March of 2012 ended up being our warmest ever March … by a LOT. Normally the 10 warmest months are separated by a few tenths of a degree, maybe one whole degree at most. That March? It beat the previous one by a whole 3.3 degrees: a statistically huge amount. For stats geeks, that’s more than half of a standard deviation for March average temperatures.
What you probably forgot by now is that it wasn’t just your normal "one-and-done" kind of warm day. It was four consecutive days of almost 80 degrees. The other three days were 79. By March standards that’s an unheard of heat wave.
Here’s some further perspective: We’ve only hit 80 in March a total of six times. Only one of those was prior to the 1960s. I repeat: In the 92 years after modern weather records began it only hit 80 in March in the Twin Cities once, but in the last 55 years we’ve done it five times.
It’s still uncommon, don’t get me wrong, but we’ve turned the dials on the climate system.
March average temperatures have warmed 2.7 degrees over the last century. Now 2.7 degrees doesn’t seem like a whole lot, but it totally shifts the extreme edges of the bell curve. Small average changes have exponential changes on the extremes, whether cold or warm (hence the curve of the bell).
Sure enough, while the average March temperature has increased from 30.4 degrees to 33.1 degrees, the average warmest temperature in March has increased from 58 degrees prior to 1947 (the midway point in our 1873-2021 historical temperature data) to a modern (since 2000) 66 degrees. That means a century ago, on average, you could count on your warmest March high temperature being 58, but now it’s 66.
A century ago the probability of having an 80-degree day in March was 1.6%, or once every 62 years on average. Basically once in a lifetime. In modern times that chance has increased to 8.4%, or once every 12 years on average.
So while 80 degrees in March is still a rare treat, it’s 5 times more likely to happen now. Our great-great grandparents would have only experienced that once in their lifetime, but their modern descendants likely will have 6 or 7 of them.
Don’t grab the shorts, flip flops and sunscreen just yet (it’s not happening this March), but know that statistically speaking it’s bound to happen in the next few years again. If it comes "as scheduled," either in 2023 or 2024, guess what? It’ll be on a weekend again, but this time it’s a choice between a Friday or Sunday thanks to leap year in 2024.
And as for that hottest March recorded in 2012? We probably won't have a March that warm in most of our lifetimes again. It was a once in an 80-year event. A century ago a March like 2012 would have been virtually impossible, a once in 1,000-year event. It's probably only happened a handful of times since the end of the last ice age 11,700 years ago.
By warming March a few degrees however, we’ve made the impossible possible.