QuickBlog

MIAMI, Okla. — Multiple injuries and fatalities have been confirmed in Greenfield, Iowa, after a catastrophic tornado laid siege to the community of roughly 2,000 on Tuesday. A swarm of tornadoes, some violent, tore across the Corn Belt and Upper Midwest, part of what the National Weather Service warned would be a “particularly dangerous” severe weather outbreak.

At least 20 tornadoes were reported Tuesday, mainly in southwestern Iowa, but more across Minnesota and Wisconsin will probably be confirmed in the days ahead. The Weather Service’s Storm Prediction Center had drawn a Level 4 out of 5 risk zone across Iowa early Tuesday afternoon, cautioning that some tornadoes could be “strong” and remain on the ground for considerable distances.

The Greenfield storm comes exactly 11 years and one day after a catastrophic tornado struck Moore, Okla. That was the last EF5 tornado on the 0-to-5 Enhanced Fujita scale to be confirmed in the United States. It’s possible that the catastrophic damage in Greenfield could earn an EF4 or EF5 rating.

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On Wednesday, the Weather Service rated the Greenfield tornado “at least EF-3” based on initial surveys of damage and wrote on X that there will be additional evaluation. “Results are subject to change,” it wrote on X.

How the Greenfield tornado became so powerful

For days, meteorologists had anticipated the formation of severe thunderstorms near and just east of the Nebraska-Iowa border because of an intense storm system predicted to sweep from Nebraska to Minnesota on Tuesday.

A complex of storms rolled through Omaha around sunrise, unleashing 60 to 70 mph winds, reports of hail to the size of billiard balls and flooding rains. By midmorning, the atmosphere was already becoming primed for a second round as a narrow filament of warm, moist air surged north ahead of an approaching cold front.

The humid air arrived as a warm front, which marked the northern edge of the soupy air, and punched north into Iowa, arriving less than two hours before the tornadoes. It’s probable that this front imparted additional low-level twist to help the Greenfield storm rotate even more violently.

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Storms began to erupt in the early afternoon just to the south, near the Missouri-Iowa border, and began to rotate as they raced to the northeast.

By midafternoon, several tornado warnings — some for confirmed “large and extremely dangerous” twisters — were issued by the Weather Service for the southwest Iowa towns of Red Oak, Villisca, Brooks and Carbon. A second rotating storm dropped another tornado near Brooks beginning at 3:07 p.m. while the Villisca tornado was still on the ground tracking to the north. A tornado near Corning eventually traveled northeast and grew into the monstrosity that would ravage Greenfield.

Inside the Greenfield tornado

A mobile DOW, or Doppler on wheels — an ultrasensitive radar on a truck — was collecting data as the tornado tore through Greenfield. It detected winds of at least 250 mph just above the ground.

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Debris was lofted to 40,000 feet — as high as many commercial aircraft fly. Debris height is proportional to tornado strength, indicating that this was an EF4 or EF5 tornado.

The Weather Service issued a warning for the twister 46 minutes before it touched down, giving residents time to shelter, probably reducing the death toll.

Damage observed in Greenfield, which includes several foundations wiped bare, would also suggest an EF4 or EF5 rating will be assigned.

That said, the National Weather Service will consult with structural engineers as they survey the damage, working to use observed damage as an approximation for wind speeds. Even if it’s known that a tornado contained winds of 200 mph or more, an EF5 rating can be assigned only if damage commensurate with that rating is found. Often, that’s quite difficult, as the majority of structures fail before winds reach those top-tier thresholds.

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Storm chaser Reed Timmer captured drone video (displayed above) depicting potent subvortexes, or smaller whirls that made up the parent funnel. Each subvortex can double the realized wind speed, since the rotational velocity of each whirl adds to that of the larger main funnel.

At one point, one of the subvortexes even had another subvortex inside it — something that’s virtually unheard of.

Jason Samenow contributed to this report.

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