Trading in U.S. corn futures is expected to start mixed Friday as forecasters predict rains will continue to disrupt planting.

In overnight electronic trading, corn for July delivery, the most actively traded contract, rose 3/4 cents, or 0.1%, to $7.49 a bushel at the Chicago Board of Trade. Corn for December delivery, which represents the crop that is being planted for harvest next fall, slipped 3 cents, or 0.4%, to $6.59 a bushel.

Ongoing concerns about planting delays should underpin prices, as rains are expected to keep farmers out of their fields across large parts of the Midwest through next week, traders said. Grain users are on edge about the slow pace of planting because farmers need to harvest a big crop to replenish inventories, which are projected to reach a 15-year low this year.

"A wet pattern suggests minimal field work into the weekend and beyond, keeping the market supported," said Stewart Peterson, a risk management firm in Wisconsin.

Corn futures reached record highs last month on strong demand for limited inventories and are down about 4% from that level. The market may set fresh highs if the weather remains poor and demand stays strong, analysts said.

Conditions will not be conducive to field work. By Saturday, rains will fall in western Illinois and start proceeding eastward, according to meteorologists at Freese-Notis Weather, a private forecaster.

"This rain starts a wet seven-day stretch of weather for the region," they said.

The July contract has had support from planting problems, as market participants are nervous the delays will postpone next fall's harvest. That could leave inventories extremely tight before farmers bring in the next crop, meaning grain users need to lock in supplies remaining from the previous harvest.

The U.S. Department of Agriculture will issue an update on planting progress in a weekly crop report Monday. Traders predict planting will be about 80% complete. As of Sunday, the crop was 63% sown, below the five-year average of 75% for that time of year.

Yet, the grains could feel pressure from profit-taking after surging recently on worries about the weather, traders noted. Corn has already climbed 10% so far this week.