By Michael Avok
OMAHA, Neb (Reuters) - Unwelcome Waves of thunderstorms dumped rain and hail in eastern Nebraska and western Iowa on Thursday and heavy rain fell in Montana this week that could make historic Missouri River flooding worse.
The Missouri has reached 30.4 feet at Omaha overnight, its second highest level behind a 1952, flood and Iowa officials said they were preparing to close parts of Interstate 29 from Sioux City to Council Bluffs by late Friday.
Bands of heavy rain fell Thursday, bringing quarter-sized hail and high winds to parts of the Omaha area. Rain is forecast for six of the next seven days.
"I'm sure to those who are monitoring how much water is being stored and released from reservoirs ... I'm sure any rainfall would be considered a concern to them," said Jim Meyer, meteorologist in charge for the National Weather Service in the Omaha area.
Meyer said a lot of the precipitation has already been factored into forecasts given to federal officials.
On Wednesday, the U.S. Army Corps of Engineers added to planned water releases from the Fort Peck Dam in Montana for a second consecutive day due to hard rains.
About 260 miles of the Missouri have been closed to boaters from Gavins Point Dam south to where the borders of Iowa, Nebraska and Missouri meet. That is near where sandbags were dropped by helicopter to patch a partial levee breach Sunday that threatens the town of Hamburg, Iowa.
From Montana through Missouri residents have been shoring up levees along the Missouri River ahead of planned record water releases from its six major dams to relieve pressure on reservoirs swollen by heavy rains and melting snow.
Maximum planned releases have been reached at the Oahe Dam above Pierre, South Dakota, and are planned to reach peaks at Fort Peck on Friday. Others will reach maximum rates by about mid June. Peak releases are planned until at least mid August.
HEAVY MONTANA RAINS
Up to five inches of rain had fallen in parts of Montana from Monday through Wednesday, forcing the Corps to increase planned releases to 60,000 cubic feet per second at Fort Peck and warn that the rate could be increased from there.
The Corps said the reservoir above the Garrison Dam had capacity to handle the additional releases from Fort Peck and has left intact its planned maximum releases at 150,000 cubic feet per second from the other five dams.
The Missouri River forms the northwest portion of the Mississippi River basin that stretches from Montana to western New York and funnels water south into the Gulf of Mexico.
The river has six dams from Fort Peck in Montana to Gavins Point on the South Dakota-Nebraska border, where it runs freely for more than 800 miles to the Mississippi River by St. Louis.
Releases from Gavins Point are the focus for people along the Lower Missouri and are planned to reach peaks on Tuesday.
The Montana rains forced fresh evacuations due to overflows on tributaries, including in Nashua downstream of Fort Peck, and in flood-battered Roundup on the Musselshell River.
Jail inmates and volunteers were placing sandbags around Ameristar Casino Hotel in Council Bluffs, Iowa, on Thursday and the parking lot of the former riverboat casino across the Missouri River from Omaha was flooded.
In Bellevue, Nebraska, just south of Omaha picnic tables were submerged and water flowed freely up to the nets on basketball hoops in an often flooded city riverfront park.
Thousands of South Dakota and North Dakota residents have voluntarily left homes in communities protected by hastily built sandbag barriers and levees ahead of peak releases.
On Thursday, officials cautioned that the sustained record flows could still threaten levees in the Dakotas now holding.
Corps officials have warned that more breaches like the one near Hamburg, Iowa, are likely given the varying strengths of the flood protections and the height, speed and duration of planned releases of water from reservoirs.
(Additional reporting by David Bailey in Minneapolis, Laura Zuckerman in Salmon, Idaho, and Kevin Murphy in Kansas City; Editing by Greg McCune)