National Weather Service staff follow the trail, seeking clues to what happened and ways to improve warnings.
Todd Krause's work began at 10 a.m. Monday in the parking lot of a Lowe's store in Coon Rapids, the westernmost point of Sunday's tornado outbreak.
From there, Krause and fellow meteorologist John Wetter would poke their way eastward in a white government van, comparing what happened on the ground to what forecasters detected on radar the day before.
Were utility poles tipped, or snapped? Did hardwood as well as softwood trees get damaged, and how extensively? How had the damaged houses been anchored to their foundations?
"I hope to learn something about the storm for the next time one comes along," said Krause, warning coordination meteorologist for the National Weather Service office in Chanhassen.
Though radar glimpses, eyewitness accounts and radar had left little doubt there was a tornado, Krause found proof right across the street from Lowe's. Small trees in a cluster had been bent, tipped and snapped inward, suggesting rotating forces of a tornado rather than straight-line wind.
Krause and Wetter, the weather service's coordinator of Skywarn radio operations, were noting and mapping damage but also taking close looks required by the new "EF" tornado damage scale, the rating that would become part of official weather history.
The process combines many elements: matching damage reports to locations, driving around fallen trees, taking pictures, waiting for escorts into high-damage zones and using diplomacy with homeowners whose homes and lives have been upended.
Krause and Wetter finally entered the most devastated part of Hugo at 3:15 p.m.
The sickening jumble of broken lumber, kitchen utensils, broken trees, a boat in a tree and pieces of glass lodged like knives in a soft foundation wall -- they all meant something to the assessors.
Where houses had been swept away, they noted that the structures had been made vulnerable by having attached garages facing the wind or walk-out basements away from the wind, or questionable ways of anchoring walls to foundations. Krause also noted that the peak of one house, otherwise wiped out, lay intact about 100 yards away. That lowered the damage rating.
In the end, Krause declared that Hugo had been hit by an EF3 tornado because the damage was consistent with winds between 138 and 167 miles per hour. But the Coon Rapids damage they'd seen earlier in the day was more consistent with an EF1, or winds of 86 to 109 mph. In between was an area of uncertainty -- an undeveloped area of Blaine from which there were no storm reports and no roads to get a closer look. So the official verdict Monday: two tornadoes, the first of Minnesota's 2008 season.
Krause said the weekend's tornadoes are no indication that the unusually destructive weather to the south this spring might be moving this way. Humidity levels might not stay high or the jet stream could leap suddenly northward, taking storm fronts away from Minnesota, he said.
From Hugo, Krause and Wetter were to continue east in Washington County on Monday night, then continue trying to confirm damage reports in Wisconsin today.
Before they left Hugo on Monday, Krause asked the owner of an obliterated house for permission to take pictures. The homeowner, Marcel Linders, gladly gave his permission.
"We heard your siren," Linders told the weather officials. "I think it saved our lives."
Bill McAuliffe • 612 673-7646