And to top it off, the last half of winter had been so cold; Nebraska had its eighth-coldest February in 124 years, Iowa its 15th. Those rivers were covered by sheets of ice up to 20 inches thick.

As runoff washed off frozen ground, it lifted the ice sheets up, broke them into huge slabs that banged downstream and eventually clogged together in ice jams, some several miles long.

Instant dams of ice.

Water surged over riverbanks into farm fields, rushed into homesteads, swept into towns. Even without ice jams, flooding would have occurred, but the jams made it all the more sudden, capricious and terrifying.

By the time it moved out, last week’s storm had stretched from Texas to Canada and from the Rockies toward the Great Lakes. Multiple states were affected not only by flooding but by blizzards, deadly fog, damaging straight-line winds, even tornadoes.

Nebraska and neighboring areas of South Dakota and Iowa were the hardest hit by flooding.