South Dakotans are used to the storms known as derechos — they’ve had two recently. What they are not used to seeing is skies turning green just before severe weather sweeps through the region.
A lawdescribed by the National Weather Service as a powerful windstorm extending for more than 240 miles, passed through South Dakota and other parts of the plains Tuesday, bringing strong winds — up to 99 miles per hour in some areas.
But before the derecho (pronounced deh-REY-cho) hit Sioux Falls, SD, the storm caused the sky to turn green, an unusual weather phenomenon. Many people on social media shared images of the green sky, which were also captured on South Dakota Department of Transportation traffic cameras.
“I think it caught a lot of people’s attention because the sky had that very unique green color,” said Peter Rogers, a meteorologist with the Weather Service’s office in Sioux Falls. “Because of the unique color it displayed, I suspect it will probably be a topic of discussion for a very long time to come.”
Unusual colors before or during a storm sometimes occur, depending on how sunlight interacts and spreads between different particles in the atmosphere, Mr. Rogers said. It is not uncommon for the sky to turn purple or even completely dark during a daytime storm.
Green skies before or during a thunderstorm can be an indicator of strong hail, according to the Weather Service. But while the color of the sky can be an indication of severe weather ahead, that’s not always the case, Mr. Rogers said.
There was no widespread hail related to the derecho on Tuesday, but the Weather Service did receive a few reports of scattered hail: A 2.5-inch hailstone was reported in Sioux Falls, and a 2.75-inch hailstone — about the size of a baseball — was reported in Lake Wilson, Minn.
In Howard, SD, about 70 miles northwest of Sioux Falls, the derecho brought winds up to 160 mph, according to the weather service† At the Sioux Falls Regional Airport, winds were blowing at 58 mph or more for about 45 minutes, peaking at 80 mph. Weather service reported†
“When you talk about wind speeds of that magnitude, it’s synonymous with a weaker tornado or a tornado on the low side,” said Mr. Rogers. “It’s tornado-like wind speeds.”
Mr Rogers said the Weather Service had received reports of damage to tree crops, power lines and some buildings. There were no reports of injuries or fatalities associated with the derecho in the Sioux Falls area.
While the green skies were unusual, the plains and the Midwest are no strangers to derechos, Mr. Rogers said.
“The residents of the area are very well aware of the potential dangers that exist with those high winds,” he said.
In August 2020, a powerful derecho destroyed several homes, destroyed crops and left more than 250,000 people without power in Iowa and Illinois. At least four deaths were associated with the storm, according to the weather service†