ROCK VALLEY, Iowa -- A storm that produced icy and snowy conditions and high winds downed dozens of electric poles and lines in Siouxland, leaving thousands without power Thursday.

MidAmerican Energy Company dispatched more than 100 line workers and support crews to repair the damaged lines in Sioux and Lyon counties and other areas of Northwest Iowa. 

The storm knocked down more than 50 transmission line poles between Inwood and Rock Valley, and 20 transmission line poles along a four-mile stretch between Sioux Center and Orange City. Transmission lines carry high voltages over long distances, and when one of them goes down, a number of people lose power. 

"In Northwest Iowa, the storm significantly damaged the electric infrastructure in several rural areas, most notably our transmission system in Sioux and Lyon counties. Those lines are part of our system’s backbone for customers in those areas," Jim Dougherty, MidAmerican Energy vice president of electric delivery, said. 

At one point Thursday, more than 3,400 MidAmerican customers were without power in Northwest Iowa. The affected areas included the cities of Storm Lake, Sheldon, Orange City, Inwood, Alvord, Rock Valley, Kingsley and other communities. 

Much of Union County also lost power due to the storm, which created blizzard-like conditions in parts of South Dakota. The Clay-Union Electric Corporation in South Dakota reported at least five poles had been toppled.

Geoff Greenwood, a MidAmerican spokesman, said Thursday afternoon that power was being restored to customers gradually, with the transmission lines of the utmost importance. 

"We've got several other situations, smaller-scale situations that we're also addressing right now," he said.

MidAmerican warned it could be a day or longer before all customers have their power restored.

The outages forced the closures of dozens of schools, government offices and businesses. In Rock Valley, city officials warned motorists to use caution "especially around major intersections that normally have functioning traffic lights."

“We’re blanketing those areas with line workers and equipment to make repairs and restore customers as soon as possible,” Doughtery said. “While we expect to restore some customers fairly soon, for others it will take longer due to the heavy damage.”

The state's largest utility began delivering portable emergency generators to customers whose service will likely be disrupted for several days. MidAmerican said it will identify those customers and contact them directly to offer that option.

The early April winter storm that moved into the region on Wednesday crippled travel in much of South Dakota and parts of Nebraska and Iowa. As much as 18 inches of snow has fallen in parts of South Dakota, including Dupree and Mud Butte. 

Galloping overhead lines were observed in many areas. Galloping, which can damage overhead lines and topple poles, can occur in high winds and icy conditions.

Much of the region was under an ice storm warning lasting until 5 p.m. Thursday. Lance VandenBoogart, a meteorologist with the National Weather Service in Sioux Falls, said a third of an inch of ice was reported in Spirit Lake. 

"The majority of that ice has already accumulated, but they might have a little bit more through the afternoon," he said Thursday. 

Due to the blizzard-like conditions, Interstate 29 shut down from Sioux Falls to the North Dakota border, and Interstate 90 closed from Sioux Falls west.

With highs in the low- to mid-40s, Sioux City and other areas to the south dodged snow and ice, but it rained much of the day Thursday.

As temperatures cooled later in the day, a mix of rain and snow moved into the Sioux City area, but the system was expected to be out of the area by midnight.

The National Weather Service predicted Sioux City would see less an inch of snow, while Yankton will likely receive up to 3 inches of new snow.

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