Chicago Board of Trade (CBOT) grains futures closed lower Thursday with wheat and soybeans futures tumbling nearly 5 percent in a technical sell-off amid outlooks for slightly cooler temperatures and chances for rain next week in U.S. Midwestern growing regions.

The most active corn contract for December delivery dropped 15.75 cents, or 3.95 percent, to 3.83 dollars per bushel. September wheat delivery fell 25.25 cents, or 4.7 percent to 5.1175 dollars per bushel. November soybeans fell 46.5 cents, or 4.5 percent, to 9.875 dollars per bushel.

Wheat, corn and soybeans extended steep losses from Wednesday that followed a U.S. Department of Agriculture (USDA) monthly supply-and-demand report showing relatively robust global stockpiles of the crops.

In its report, the USDA pegged the U.S. 2017/2018 corn ending stocks at 2.32 billion bushels vs. the average estimate of 2.181 billion bushels and last month's 2.11 billion.

The USDA sees U.S. 2017/2018 soybean ending stocks at 460 million bushels vs. the trade's estimate of 495 million bushels and USDA's June estimate of 495 million.

U.S. 2017/2018 wheat ending stocks are pegged at 938 million bushels vs. the trade's estimate of 876 million and USDA's June estimate of 924 million.