Tornadoes in Minnesota explained: Frequency and detection

It’s kicking off a few days early this year, but Minnesota’s tornado season, traditionally May through September, is upon us. While we won’t know the true power of the latest storm or its aftermath until the winds have come and gone, Minnesotans braced for a day of high winds, rain, and “radar-indicated rotation.”

“We have a confirmed touchdown in Martin County, so we will have tornadoes; we just don’t know how many,” Department of Natural Resources assistant state climatologist Pete Boulay told MinnPost late Monday afternoon. 

While tornadoes are powerful, Boulay said that from a safety perspective, “I would be more wary of the lightning, the hail, the winds than anything specific to the tornadoes.”

Minnesota sits along the northern edge of what is known as “Tornado Alley,” the DNR says. The occasional tornado is something Minnesotans have gotten used to – the state hasn’t had a year without at least one tornado for over seven decades, the DNR points out, with most years seeing a couple dozen twisters in the state. And while this is a bit early, Boulay said that it is not unheard of to have tornadoes in April, though the summer months offer more moisture that twisters can feed off of. 

The state’s experience with tornadoes means that officials broadly know what to do to mitigate the threats to life and property during these situations. Some school districts took  precautions such as shuttering buildings early or canceling after-school activities.

Despite that, there remain dangerous myths and half-truths out there. Chief among them is that tornadoes somehow “avoid” downtowns and built-up urban areas. Tornadoes and other major thunderstorms have struck both Minneapolis and St. Paul, and the DNR notes that a tornado most recently reached Minneapolis on Aug. 19, 2009. Since 1950, every one of Minnesota’s 87 counties has experienced at least four tornadoes, with two northwestern counties seeing around 80 over that time period. Otter Tail, Polk and Freeborn counties have recorded more tornadoes than other counties.

There does seem to be evidence that tornadoes are becoming more frequent, though it is far from decisive. A study from the National Severe Storms Laboratory said that “a significant upward trend in tornado frequency was found in portions of the Southeast, Midwest, and Northeast” over the years 1979 to 2017, as quoted on this National Weather Service site. However, the NWS itself points out that the study was not conducted by its own scientists, and they were simply sharing the highlights of other researchers’ findings. 

Additionally, the National Oceanic and Atmospheric Administration (NOAA), put out a brief explainer on “Tornadoes and Climate Change: What Do We Know?” that effectively said that it is difficult to attribute any change in tornado activity to climate change.

Boulay’s take on climate change’s effect on tornadoes hews closely to the idea that we don’t have enough information to confirm any attribution to climate change. 

“Looking at tornadoes you need two ingredients: You need more juice and more shear. With climate change we’re getting more moisture, that’s the juice. But we’re not getting any more shear, which is the spinning of the winds. Climate change might give us more rain but not necessarily more tornadoes,” he explained.

When we look back at the number of tornadoes recorded in Minnesota since 1950, it would appear as though their frequency has skyrocketed, whether due to climate change or other reasons. But these numbers should be taken in the context of their times. There are plenty of reasons for variation over the decades, such as improvements in tornado-tracking technology and recording since the ‘50s. Back then, we didn’t even have satellites, whereas today, there are 322 Earth-observation satellites in orbit, according to the World Meteorological Organization, many of which watch out for tornadic weather. 

There have been other jumps in technology as well. The widespread use of radar in the 1970s allowed scientists to see storms as they built up strength, but did not help much with identifying tornadoes specifically, which often hide inside of a thunderstorm, Boulay said. The big leap forward though came with Doppler radar, which came into use in the 1990s.

“That was really the game changer, so you can see the tornado inside the storm now,” Boulay said of Doppler. A similar, though less significant, effect occurred in the 2000s when cell phones with cameras allowed anyone to record and report a tornado, though trained tornado spotters still remain a critical link in the chain to confirm tornado touchdowns, Boulay added. 

All of that is to say that Minnesota may not be experiencing more tornadoes now than in the past, but is simply better able to record the tornadoes that do happen. With that significant caveat in mind, there is still value for scientists in keeping track of the numbers of recorded tornadoes, especially from 1990 onward, according to Boulay.

And he gives a final word of warning for Minnesotans: “Keep an eye to the sky. Tornadoes are part of our climate.”