A wind turbine tower is a tube, not a post.
It carries the machine on top by keeping its own wall in tension and compression, and that wall is thinner in proportion than the skin of a drinks can.
Thin walls do not snap.
They buckle, which means a dent forms on the compressed side and the whole section folds through it in a fraction of a second.
That is what happened in Iowa.
Rows of steel towers went over in one afternoon, and the tornado that did it was still being measured as it passed.
Why a tornado is not simply faster wind
A turbine is built for a direction.
The rotor turns to face the wind, the blades feather to spill it, and every load path in the tower assumes the push arrives from one side at a time.
A tornado removes that assumption.
The flow rotates, so the direction of the push swings through a full circle in seconds and the tower is loaded from angles it never saw in testing.
There is also lift.
Air inside a tornado moves upward as well as around, which adds a vertical component to a structure designed almost entirely for sideways force.
What was standing on that ground
The machines were not experimental.
The damaged sites ran two megawatt units from a Danish manufacturer, a workhorse design installed by the thousand across the American Midwest.
The rotor is the giveaway.
Blades on that model sweep a circle about 361 feet across, which is an enormous amount of surface for a moving air mass to catch hold of.
The towers went down in a line.
Survey crews found the flattened machines strung along a corridor of seven to eight miles, which traces the damage path rather than a series of unrelated failures.
Design wind speed is the reference point.
Machines of this class are built to ride out gusts near 120 miles per hour, and the engineer who refined the damage scale puts the toppling threshold at 140.
Nothing about the sites was unusual.
Two of them sit in Adair County on ordinary farm ground, in a state that ranks second in the country for installed wind capacity.
The numbers the storm left behind
The official rating came from damage.
Surveyors put the tornado at the fourth step of the intensity scale with winds around 185 miles per hour, which is the standard method and a conservative one.
A radar truck happened to be there.
A mobile Doppler unit scanning every seven seconds recorded between 308 and 318 miles per hour at roughly one hundred feet above the ground.
That reading is not the whole tornado.
The peak sat in a narrow band on one side of the circulation and lasted under a second at any given point, which is long enough to start a buckle.
The storm was on the ground for 48 minutes.
It ran 42 miles from beginning to end and grew to nearly a mile wide at its broadest, which is how it managed to cross more than one wind farm.
The turbines reported too, briefly.
Sensors on several machines logged winds above 100 miles per hour and then stopped transmitting, so that figure marks where the instruments quit rather than where the wind stopped.
The count that keeps getting left out
Six is one company’s share.
The same tornado also took down four more turbines at a third site in the next county, owned by a completely different operator.
The real total is ten.
Ten machines across three wind farms in two counties, which is a larger event than the figure most coverage settled on.
The engineering account is harder to check.
A journal study of these failures exists and the paper sits behind a paywall, so nobody quoting its conclusions in public has shown the working.
The field evidence points one way.
The forensic engineer who walked the site said the blades came apart first and the tower held longer, which is the same order seen when one blade fails on a calm day.
What six towers out of thousands means
The operator called it unprecedented.
That word is doing real work, because the company has run wind farms since 2004 and had lost exactly one turbine to a tornado before this.
The denominator matters.
Six losses came out of a fleet of more than 3,400 turbines across 34 counties, and the operator keeps that number public.
The failures are becoming useful.
Damage surveyors are adding turbines to the intensity scale as a formal indicator, because a folded tower says more about the wind than a blade that simply stops turning.
None of it changes the design.
A tower built to survive a direct tornado hit would cost far more than the losses it prevents, so the economics point at rebuilding instead.
Which leaves the honest reading.
Six steel towers folded because a rotating wind found a thin wall, and the machines that did not fold were a mile away.
