Minnesota's winter low temps continue rising

If Minnesota winters seem warmer than when you were a kid, you're not imagining it.

The statewide average low temperature for December-February this year came in at 11.8 degrees, a marked difference from years past. This continues a decades-long upward climb in winter low temperatures that scientists attribute to climate change.

Sure, there are winters (like 2013-14) that have been phenomenally cold, and certainly this year's spike could prove to be an anomaly. But even without those outliers, there has been a clear upward trend in the average low temperatures that has been most prominent in the past 35 years.

Choose a region to display the average low temperature over time:

During the first 16 years of the 20th century, only six Minnesota winters had an average low temperature above zero. In the same time period this century, we've had 13 winters with an average above zero. The change is especially striking in the Northeast region.

The low temperature readings are creeping up in all months of the year and throughout the United States, but it's most evident in winter and places that experience it the most dramatically -- like Minnesota.

"The farther north you go, the stronger you see this," says Kenny Blumenfeld, a climatologist in the State Climatology Office of the Minnesota Department of Natural Resources.

Blumenfeld explained that this warming trend is most noticeable in winter because times of limited sunshine are when earth typically loses the most heat, resulting in lower temperatures. But greenhouse gases act like a blanket, preventing the heat from leaving.

This blanket is also holding back the extreme low temperatures we typically saw in the winter. Up until the mid-1970s, it was relatively common to have one or more days each winter dipping down to -25 or lower in the Twin Cities. But the Cities haven't sunk that low since 1996-97, when it hit -27.

But something else that's playing a role in the rising low temperatures, especially in the Twin Cities, is a phenomenon known as the "heat island" effect.

Just look at the low temperatures recorded each year in the Twin Cities versus those recorded in St. Cloud. It's typically 5 to 10 degrees warmer in the metro area, where denser development and pavement make it warmer.

One unanswered question, says state climatologist Pete Boulay, is whether the recent rise in coldest temperatures in St. Cloud might be due to this "heat island" effect creeping north.

A program at the University of Minnesota, called "Islands in the Sun," is researching this phenomenon, aiming to provide suggestions for minimizing this effect in the future. (The program is looking for homeowners willing to host temperature sensors in their yards. More information is on their website.)

For those who love a hot summer, the bad news is that the maximum temperatures in July are one of the only temperature metrics not going up, Blumenfeld said. But he added that we should probably tack the word "yet" onto the end of that sentence.

We haven't been hitting the big triple-digit temperatures in the summer lately because of high moisture levels, which puts a limit on both how hot or how cold it can get. But that could change.

"Some of the models suggest that by the time we get to the middle of the century, parts of Minnesota may have five to 15 additional days above 95 degrees each year," Blumenfeld said.

Data source: National Oceanic and Atmospheric Administration's Climate at a Glance.
Data Drop is a weekly feature that uses data analysis and visualizations to explain, surprise, inform and entertain on topics relevant to Minnesotans. Do you have an idea you'd like us to explore? Contact MaryJo Webster