USDA now forecasts U.S. farmers will harvest 13 billion bushels of corn this fall, with yields averaging 164 bushels per acre. The latest Crop Production report, released last Friday, reflects slight increases from last month's predictions in yields and total production and an 8 percent larger harvest than last year.

The 164.2 bushel per acre average yield would be the highest on record and total production will be second only to the record set in 2007.

Yet, cooler-than-normal weather could still play a role in that. Snow and frost over the past week have effectively put an end to the growing season across much of the Corn Belt. Harvest delays and the recent freeze are expected to trim yields and negatively affect crop quality.

As of last Sunday, the corn harvest was 13 percent complete, according to the USDA, compared to 20 percent at the same time a year ago.

Marty Foreman, senior economist with Doane Advisory Services in St. Louis, said Tuesday that the commodity markets have pretty well priced in the freeze damage, and they will now be focused on the weather for harvest — and whether there will be harvest delays.