CHICAGO (Dow Jones)--U.S. corn futures are expected to start stronger Wednesday after a well-known crop forecaster projected output will drop 4.3% from last year.

Traders predict corn for December delivery, the most actively traded contract, will open up 3 cents to 6 cents a bushel at the Chicago Board of Trade. In overnight electronic trading, the contract rose 6 1/2 cents, or 0.9%, to $7.62 1/4 a bushel.

Driving prices higher was a surprisingly low output estimate from Cropcast Ag Services, a private weather firm. The company estimated corn output at 11.913 billion bushels, 7.8% below the U.S. Department of Agriculture's latest estimate and down 4.3% from last year.

The forecast surprised traders as it came in below other estimates from other forecasters, who have been issuing estimates in advance of a monthly USDA crop report Monday. Informa Economics, a closely watched forecaster, on Tuesday estimated the corn harvest at a much larger 12.711 billion bushels.

The USDA is expected to lower its harvest estimate Monday due to hot, dry weather that stressed the crop this summer. The government raised expectations for the downgrade by lowering its good-to-excellent rating for the crop by two percentage points to 52% in a weekly report Tuesday.

"Continued moisture deficits can still put the focus on the crop," said Rich Nelson, director of research for Allendale, a brokerage firm in Illinois.

Traders are on edge about the size and quality of the upcoming harvest because inventories of corn are historically low. The December corn contract has pulled back about 2% since reaching a contract high last week on supply fears.

Weakness in the U.S. dollar should help boost grain prices, as it makes U.S. commodities more attractive to foreign buyers, traders said. A rebound in equities and crude oil should add support, they noted.