CHICAGO Jan 7 (Reuters) - The U.S. Midwest and Plains remained in a deep freeze on Tuesday with sub zero temperatures at record or near-record lows, raising the risk of winter-kill damage to dormant wheat along the Ohio River valley, meteorologists said.
Overnight lows fell to -5 to -10 degrees Fahrenheit (-20 to -23 Celsius) across southern Indiana, Ohio, Illinois and northern Kentucky - big soft red winter wheat country, where much of the area was unprotected by snow cover.
"It was cold enough to put about 5 percent of the soft wheat crop at risk," Joel Widenor, an agricultural meteorologist with Commodity Weather Group, told Reuters.
Snow cover protects dormant wheat when temperatures dip below zero and persist for four hours or more. Without sufficient snow cover, damage to exposed wheat can prevent the crop from reaching its full yield potential next summer.
The central Plains hard red winter country was warmer early Tuesday, with lows in the single digits up to the 20s F, a big contrast from the -10 to -20 F readings on Monday, when up to 30 percent of the Plains wheat belt was at risk of winter kill, agricultural meteorologists said.
The frigid temperatures and weekend snows also slowed livestock and grain shipments through the heartland and curbed meat production at several packing plants.
Indiana Packers Corp in Delphi, Indiana, said in a statement that plant operations remained suspended Tuesday due to hazardous roads and brutally cold temperatures, but the facility was expected to resume full production on Wednesday.
Two Cargill Inc beef and pork plants were running at reduced levels because of road conditions that slowed the transport of hogs and cattle, said Cargill spokesman Mike Martin.
Several flour mills in New York and Ohio were closed Tuesday as poor weather slowed rail and truck movement of grain, cash grain traders said.
The Illinois River, a major artery to ship grain, remained open to barge traffic on Tuesday, but traffic was restricted to one-way only along a 10-mile stretch near Peoria, Illinois, due to ice buildup, the U.S. Coast Guard said.
Barge shippers were breaking up surface ice to keep the navigation channel open, Coast Guard Lieutenant Colin Fogarty said. However, ice floes were stacking up at locks and dams and freezing together in much larger blocks, known in river parlance as gorging, and that can make lock and dam gates difficult to open and close.
Cash basis bids for soybeans shipped by barge to Gulf Coast export elevators jumped to the highest in four months, in part because of ice-slowed shipments from the Illinois and traffic backups on the Mississippi River around St. Louis due to low water.
Temperatures in the upper Midwest fell to the minus teens F and wind chills of -35 to -40 F.
But temperatures were forecast to rise into the 20s to 30s F later this week, with some southern Midwest locations possibly seeing highs in the 40s F, according to forecasters.
"Most of the snow came to an end yesterday, so transportation should be improving," said meteorologist Andy Karst with World Weather in Kansas City.
"Another storm is headed to parts of the Midwest Wednesday into Thursday and again on Friday into Saturday - it's not going to be a big deal."