Expert says warm nights could aggravate flooding Melting of heavy snow still on the ground may bloat waterways. Iowa's first widespread spring flooding is expected to begin today as a one-two punch of melting snow and spring rain rushes the state's rivers. The National Weather Service expected scattered streams to slip out of their banks. Immediate major damage was unlikely, but the heavy snow still on the ground in the northern counties and upstream in Minnesota threatens to bloat rivers to the danger point, especially in northern Iowa, forecasters said.
Many rivers already are high.
Nighttime temperatures above the freezing mark. Lower temperatures at night re-freeze the snow melted by warmer daytime weather, slowing the runoff. Most of the soil in Iowa is already fairly wet. If the melt comes quickly, the water would run off instead of soak in. Consistently cold temperatures that keep the snow from melting at a slower pace.