Wet weather is expected in most of the U.S. Midwest this week, slowing a corn planting pace that already has fallen to a record low level, an agricultural meteorologist said on Monday.

"It's going to be slow going. Already the west is seeing 1.0 to 1.5 inches in a widespread area, and that will spread into the eastern Midwest early this week," said John Dee, meteorologist for Global Weather Monitoring.

Dee said the rains would continue into mid-week, followed by a few days of drier weather. But more rain is expected Saturday through Tuesday, with the heaviest amounts in roughly the northern half of the Midwest.

"The rain will favor areas generally north of Interstate 80, but it will include most of Iowa. So it looks like for the next week to 10 days they won't get much done in Iowa," he said.

Iowa and Illinois are the two largest corn- and soybean-producing states in the United States.

Drier weather last week allowed farmers into their fields, and rapid seeding progress is believed to have been made. Some observers expect planting to be 50 percent to 60 percent complete by now, but still at a record slow pace.

A week ago farmers had seeded 28 percent of their intended corn acres, up from 12 percent a week earlier but far behind the five-year average of 65 percent, the U.S. Department of Agriculture (USDA) said in a weekly report released last Monday.

The planting pace was the slowest for this point in the year in USDA records, dating back to the 1980s, and was below the average estimate of 29 percent from analysts surveyed by Reuters ahead of the USDA report.

For soybeans, the USDA said planting was 6 percent complete, up from 2 percent a week earlier. But the pace was the slowest for the 19th week since 1984, when soybeans were only 4 percent seeded. The five-year average is 24 percent.

USDA will release updated corn and soybean planting data in its weekly crop progress late on Monday.