The National Weather service issued a preliminary report indicating extraordinarily wide and long-running tornados were responsible for the damage in Comfrey, Le Center, and St. Peter on March 29, 1998. The review identified a total of seven seperate tornadoes which hit Brown, Nicollet, Le Sueur, Rice, and Dakota counties. Two, or possibly three, of the tornadoes were especially destructive "multiple vortex" tornadoes.
Frequently referred to as the 1998 Comfrey–St. Peter tornado outbreak, 14 tornadoes (including an F3 & F4) wrought destruction in southern Minnesota on March 29, 1998. More than 3,000 buildings were damaged or destroyed by the tornadoes. The towns of St. Peter and Comfrey were utterly devastated. Storms left two people dead and dozens injured.
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BILL CATLIN: The National Weather Service report addresses questions that have hovered over the massive damage inflicted on areas of Southern Minnesota. How many and how severe were the tornadoes that did this? The report found Comfrey, LeCenter, and Saint Peter were each devastated by one of three separate tornadoes.
The tornado, which leveled much of the small town of Comfrey and killed an elderly farmer, was one of the two most severe tornadoes. Based on initial observations, the Weather Service said the tornado's destructive path extends 36 miles in length. Most tornadoes don't go more than one third that distance. Airborne observations conducted yesterday afternoon showed the tornado's path is actually much longer 62 miles. Comfrey falls roughly in the middle.
DAN MILLER: I'm amazed, but I'm not surprised.
BILL CATLIN: Weather Service meteorologist Dan Miller was on duty when the tornadoes hit Sunday, and watched them on radar. Over the next several days he helped compile the new report. He says a tornado that traverses 62 miles is not unheard of, but he says it's very rare.
DAN MILLER: To get a tornado on the ground to sustain itself for that length of time is pretty incredible by any standards, even for anywhere in the Eastern 2/3 of the country, including Tornado Alley down in Oklahoma and Texas.
BILL CATLIN: The tornado that hit Saint Peter, killing six-year-old Dustin Schneider, was also a so-called long-track tornado beginning to the Southwest of Saint Peter and traveling 18 miles. Both the Comfrey and Saint Peter tornadoes were a mile and a quarter wide, several times wider than usual. Tornadoes generally don't exceed several hundred yards in width. Miller says each had multiple vortices.
DAN MILLER: There's just this wide, massive circulation, which is on the ground, maybe a mile to a mile and a quarter wide. And in addition, the whole thing is rotating itself but then there's these little vortices which are all spinning around one another. And they are the most violent, and they tend to do the most damage and also be the longest in longevity.
BILL CATLIN: Miller says some of the most severe damage occurs along the path of the smaller vortices that crop up.
DAN MILLER: Those wind speeds are also supporting unbelievable amounts of flying debris in the air, which actually does quite a bit of the damage as well.
BILL CATLIN: Miller thinks there's a strong possibility the third tornado, which hit LeCenter, also had multiple vortices. The Comfrey and Saint Peter tornadoes were rated F3 on the Fujita scale, a system of grading tornadoes based on the severity of the damage they cause to a well-constructed building, such as a house.
The scale runs from F0 at the low end to F5. Miller says an F5 tornado would strip a house from its foundation and pulverize the structure beyond recognition. He says that occurred in the 1992 tornado that hit Chandler, Minnesota. He says most of the damage from Sunday's tornadoes did not exceed the F3 level.
DAN MILLER: At least some walls standing. Now, that doesn't necessarily mean exterior walls, but there are usually some walls still standing on the house. Maybe the entire second story of a house may be gone, but the bottom part is still there and it's usually still on its foundation.
BILL CATLIN: Miller says he saw several houses torn from foundations with recognizable pieces strewn nearby, suggesting F4 damage, but the construction was questionable.
DAN MILLER: One of the homes didn't appear to be attached to the foundation by much more than just some short nails or things like that. And by definition, that's not a well-built structure according to the way the Fujita scale was developed.
BILL CATLIN: Only the Saint Peter and Comfrey tornadoes were rated F3. Miller says their winds probably exceeded 160 miles per hour, but he's skeptical of attempts to translate the Fujita scale into a measure of wind speeds. The tornado, which hit LeCenter in Le Sueur county was rated F2. It had the third longest track at 17 miles and was 1 mile in width.
The other four tornadoes were in Rice and Dakota counties, two each ranging from F0 to F2, and from a brief touchdown to a 5 mile track a quarter mile wide. Except for the Comfrey tornado, the report did not review other tornadoes, which affected Nobles and Cottonwood counties. Those areas are in the jurisdiction of the Sioux Falls office of the Weather Service, which has not yet completed its review.
Miller says the Weather Service compiles the reports for several reasons. It's part of an ongoing effort to study tornadoes, improve warning systems, and prevent loss of life. And, he says, the media, the public, and federal emergency agencies want an authoritative analysis of what caused so much havoc. For Minnesota Public Radio, I'm Bill Catlin.