U.S. soybean futures are expected to start lower Thursday as lower-than-expected weekly export sales fuel concerns about poor demand for the oilseed.

Traders predict soybeans for November delivery, the most actively traded contract, will open 3 cents to 5 cents a bushel lower at the Chicago Board of Trade. In overnight electronic trading, the contract slipped 2 1/2 cents, or 0.2%, to $13.80 1/4 a bushel.

Weighing on prices will be data from the U.S. Department of Agriculture that shows exporters struck deals to sell just 351,900 tons of soybeans to foreign buyers in the week ended Sept. 8. Traders had been expecting sales of at least 400,000 tons and as much as 600,000 tons.

The lackluster demand increases concerns about waning demand from China, the world's top soybean importer. China has increasingly shifted its business to South America from the U.S.

"Export sales were on the light side," Benson Quinn Commodities told clients in a note.

Traders are keeping a close eye on sales after the USDA on Monday raised its export outlook for the upcoming year in a monthly crop report. Some traders expect demand to increase in the short term as prices have pulled back nearly 6% since the November contract topped a three-year high in late August.

Prices may continue to pull back as the U.S. harvest begins in the Midwest in the next few weeks, attracting more buyers to the market, traders said. Some were encouraged when the USDA said Wednesday private exporters had sold 106,000 tons of soybeans to China.

"The Chinese are notorious for buying on weakness, so maybe we have gotten prices low enough to attract them back to our market," said Tomm Pfitzenmaier, analyst for Summit Commodity Brokerage in Iowa.

In other news, there were conflicting opinions about cold weather that threatened to hurt crops in the northern Midwest. AgResource Co., a well-known agricultural consultancy in Chicago, said temperatures were not as cold as initially feared. Freese-Notis Weather said the cold snap met expectations, with lows of 32 degrees or colder "quite common" in northern Iowa, Minnesota, western Wisconsin, and eastern parts of North and South Dakota.