A supercell thunderstorm struck the Brainerd lakes area Sunday night with a force nearly matching a category 1 hurricane.
A supercell thunderstorm is potentially the most dangerous of convective storm types, the National Weather Service reports. The storm itself is so powerful it rotates. Supercell storms have the potential to generate violent and long-lived tornadoes and downburst damage. The downburst, a strong downdraft producing damaging high winds on or near the ground, is the culprit in causing the damage in the Brainerd lakes area, the National Weather Service reported.
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A meteorologist assessed the damage in the lakes area before determining the downburst, which may also be called straight-line winds, was the factor here not a tornado.
The main damage path was 8 miles long and 3 miles wide.
"Straight-line winds can do tremendous damage and you don't need a tornado to get the kind of damage that you experienced," the National Weather Service posted on its Facebook page in response to inquiries from the Brainerd/Baxter area. "The Boundary Waters derecho in 1999 was much larger in scale and was due to straight-line winds."
The National Weather Center in Duluth was monitoring the region, expecting storms to develop as a potent combination of storm-building ingredients came together. The tone for the day was set in the morning. The Storm Prediction Center in Norman, Okla., listed the Brainerd lakes area in a moderate risk for thunderstorms.
Melody Lovin, meteorologist with the National Weather Service in Duluth, said in weather terms a moderate risk is significant and comes with an expectation for tornadoes.
"Whenever there is a slight risk we are watching it very, very closely," Lovin said.
Sunday's storm developed after a warm, oppressive and overcast day. High atmospheric instability and wind shear produced the energy needed to create the massive storm. Instability means there is a lot of energy and potential for rising motion and it's the wind shear that allows it to develop rotation and become severe.
"It was kind of a loaded gun situation as far as the atmosphere coming together to produce these type of strong storms," Lovin said.
"We tend to get storms like this once or twice a season," Lovin said.
Much of the damage was west and north of Brainerd with tornadoes by Otter Tail and close to the North Dakota and Minnesota state line.
"There was widespread damage reported," Lovin said, noting storms moved from Fargo, N.D. to Milwaukee, Wis.
In the lakes area, the radar's intense red of the storm first appeared to be going north. But the storm then appeared to turn.
"With very strong storms they tend to take a right turn. That's something we watch closely because when they tend to take a right turn that indicates it is getting stronger because it is getting more rooted in the upper atmosphere," Lovin said.
Lovin said every storm with updraft has a little rotation to it and determining what caused damage includes looking for patterns. It doesn't have to be exact but if the overall pattern matches, Lovin said it can be scientifically proven to be straight-line winds or a downburst.
"Some people in the area were very staunch in saying that it was tornado damage and I would say it's important to realize that a 70 mph wind whether it's twisting in a tornado or just straight-line it's very damaging. It doesn't need to be in the form of a tornado to cause extensive damage and a threat to life and property."
Lovin said equipment measured the winds here up to 65 mph with gusts higher for an estimated range of 65 mph to possibly 80 mph. A category 1 hurricane has winds of 74 mph to 95 mph. If the storm's winds reached 100 mph, Lovin said the damage would have been significantly more severe.
The temperature dropped from 81 degrees to 64 degrees in the aftermath of Sunday's storm.
Storms blew up again late Monday afternoon with thunder rumbling through the lakes area and heavy amounts of rain. For those faced with the task of cleaning up storm debris, the weather service noted the chance for severe weather continues Thursday, Friday and into next week. The chance for thunderstorms is listed at 50 percent Thursday with a chance Thursday night before giving way to mostly sunny skies Friday.
Expect warm temperatures to continue with highs in the 80s, climbing to a high of 87 Friday and 88 Saturday.
Lovin said a typical summertime pattern is setting up. "This is usually our prime time for thunderstorms, of course."
(This story was corrected to note another storm blew in Monday and some of the heaviest storm damage was to the west and north of Brainerd.)