After a severe storm system traversed over the metro on May 25th, MPR’s Tom Crann discusses tornado science with meteorologist Paul Huttner, who explains the importance in distinguishing between straight line winds and a tornadic storm for climatology analysis.
On May 25, 2008, supercell thunderstorms produced large hail and tornadoes from the northern Twin Cities metro area to western Wisconsin. Four tornadoes touched down in Minnesota. The strongest tornado was an EF-3 which hit Hugo, Minnesota. The EF-3 tornado packed winds up to 165 mph, destroyed trees, houses, barns, and silos. Two-year-old Nathanial Prindle was killed, and nine others were injured.
Transcripts
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TOM CRANN: Good afternoon. 4:45. I'm Tom Crann. We're going to get some perspective now on the storms and the situation in the Northern Metro from Coon Rapids to Hugo, from meteorologist Paul Huttner who joins me.
And Paul, I'm a bit confused here first, and that is we know now from the National Weather Service that the Coon Rapids storm, the damage there has been done by a tornado. But do we know is that the same storm that we saw the damage from in Hugo?
PAUL HUTTNER: It is, Tom. This was a single, rather large tornadic supercell thunderstorm that moved through the North Metro late yesterday afternoon. And what can happen in these situations is the parent thunderstorm develops that rotation, that mesocyclone, and that can produce a tornado that may touch down for a bit and then lift back up into the Cloud and then touch down again, perhaps at multiple points.
So it was that same storm that went through Coon Rapids and Hugo. Now, whether or not the tornado was continuously on the ground between Coon Rapids and Hugo or whether it touched down in Coon Rapids and then lifted up and touched down in Hugo again, that's something the National Weather Service team is looking at out there today.
TOM CRANN: So it is possible then, that one storm could travel that distance, although not necessarily on the ground. And then there were a lot of other incidents in the North Metro. Were there any others that we know about or were likely to hear about that might have been tornadoes?
PAUL HUTTNER: Well, this one storm, Tom, was really developed up over Wright County, and they were out there earlier today. Todd Krause and his survey team from the National Weather Service, and they determined the Wright County damage. And this is out around Silver Lake was not tornadic, that it with straight line winds out there.
But this was the same supercell thunderstorm. This thing held together for almost two hours at least, and then moved through northern Hennepin County and then became tornadic around Coon Rapids. And I'm looking here at the hook echo archived on the National Weather Service site of this storm. This is a classic textbook storm.
This is exactly what they teach us in meteorology, coursework, and seminars that we go to of what to look for to define a tornado. And this thing rumbled right through Anoka County then, and all the way into Washington County before it went into Wisconsin, as it still held together that single tornadic supercell thunderstorm.
TOM CRANN: Last time we talked, we talked about what they do on the ground, and they look at basically the physics of the way-- if there's destruction, the way it happened. And they can tell, what about, do they recreate somehow the air conditions or the conditions above ground as well to try to get to the bottom of what happened?
PAUL HUTTNER: They will look at the radar images from yesterday, the Doppler radar and the reflectivity as well, to try to help determine that. But a large part of the work they do will be on foot, on the ground, surveying the damage patterns.
Do they go in the same direction? Are trees blown down in the same direction? Or is it scattered in multiple directions? And that's how they'll determine straight line winds versus tornado. And then the next thing they do is they say, OK, it was a tornado, which Todd Crosby confirmed today from our local National Weather Service office out in Coon Rapids and Hugo.
How strong were the winds? And that's where the EF scale comes into play. And they will look at how the structures were damaged and then estimate the wind speeds on a 3-second gust from that damage.
TOM CRANN: Now, whether or not it is straight line winds or a tornado, if your house is destroyed or badly damaged, that seems like an academic distinction. So why is it important that we know the difference and know exactly what happened here in a way, forensically?
PAUL HUTTNER: Well, first of all, you're absolutely right. And of course, we feel for the people. It doesn't matter whether it's straight line winds or a tornado that damages your home. But it does matter in terms of statistics.
For one thing, we keep track of the number of tornadoes. That helps us create tornado climatology over time and over the years to find patterns within tornadoes. Those are the main reasons to keep track of whether it with straight line winds or a tornado. And it's instructive and it helps us further analyze these storms as they come through.
TOM CRANN: In general, the storm system you saw yesterday, something extraordinary for this time of year?
PAUL HUTTNER: Pretty typical, Tom. I would say late May, early June, that's prime severe weather season for us. It's prime tornado season here in the upper Midwest. The remarkable thing to me was there were other supercells around.
This is the only one in the Twin Cities, thankfully, that turned tornadic yesterday. It wasn't a family of tornadic supercells like we had back in 1965. So we got off a little lucky there. We dodged a bullet. And also had this been about 10 miles farther South, it would have come right through downtown Minneapolis and Saint Paul.
TOM CRANN: All right. Thank you. Meteorologist Paul Huttner with us at 4:50.