"Iowa's corn yields could be cut in half where hurricane-force winds flattened fields"

The tornado warnings and knocked-over trees in Chicago got the headlines but it looks as if the real damage was done in Iowa.
From the DesMoines Register, August 12:

Yields may be cut by as much as half where a derecho flattened crops as it swept through Iowa this week, agriculture officials said.

Iowa Agriculture Secretary Mike Naig said in a call with reporters that no other Midwestern state along the storm's 770-mile path suffered the level of wind or hail damage that struck an estimated 10 million acres across central Iowa.

That's about a third of Iowa's 30 million acres of crops — acreage typically split between corn and soybeans in Iowa, the nation's largest corn producer.

The derecho's straight-line winds reached nearly 100 mph in parts of Iowa, officials said. The storm swept across Nebraska, Iowa, Illinois, Indiana, Wisconsin and Michigan before losing steam....

....MORE 

Yesterday's WASDE report predicting a record U.S. corn harvest overshadowed the storm damage but it appears word is getting out this morning, CME 30-minute prints: