U.S. corn futures are expected to start mixed Friday as traders catch their breath after prices surged Thursday on a smaller-than-expected harvest estimate.

Corn for December delivery, the most actively traded contract, finished unchanged at $7.14 a bushel in overnight electronic trading. The market stabilized following a 3.7% climb Thursday at the Chicago Board of Trade.

Traders are assessing the outlook for the crop after being surprised Thursday by a deeper-than-expected cut in the U.S. Department of Agriculture's harvest estimate. The department, in a monthly report, slashed its output forecast 4.1% from July, to 12.914 billion bushels, due to intense heat that damaged the crop.

Yet, the forecast was "only a starting point" in the debate on output, according to AgResource Co., an agricultural consultancy in Chicago. Traders are now determining how August weather could influence the crop before the USDA issues its next output estimate in September.

AgResource said it was leaning toward a modest decline in USDA's September yield estimate, noting that warmer-than-normal temperatures and below-normal rains were not ideal for crops in parts of Illinois and Iowa in the first half of August. Temperatures have turned milder recently, and rains are expected in the Midwest this weekend.

Yet, the impact of favorable weather will be more limited for the crop because the key development period for corn was in July. Traders will keep a close eye on weekly crop-progress reports from USDA, issued on Mondays, to see whether conditions continue to deteriorate.

"The trade is expecting that crop condition rating next week to show more decline, and traders may be content today to sit on their hands today and wait until next week," Iowa-based Summit Commodity Brokerage told clients in a note.

In other news, China raised its output forecasts for key grain sectors Friday, increasing its outlook for corn by 3% from last year to 182.5 million metric tons compared with a July forecast of 181.5 million tons. The size of China's harvest is important because the country may increase its imports of U.S. corn if output is disappointing.