CHICAGO, Feb 15 (Reuters) - U.S. corn and soybean futures weakened further on Thursday, setting fresh three-year lows as abundant supplies hung over the markets.

Traders are assessing inventory and production forecasts for the next crop year, after U.S. farmers brought in a record corn harvest in 2023 and shoved much of it in storage bins.

At its annual outlook forum, the U.S. Department of Agriculture predicted U.S. corn stocks would balloon about 17% from the end of the 2023/24 marketing year to 2.532 billion bushels by the end of 2024/25. That would be the most since 1987/88.

Soybean ending stocks are expected to climb 38% to 435 million bushels by the end of the 2024/25 marketing year, the highest since 2019/20, the USDA said.

Analysts had projected 2024/25 soybean stocks at 411 million bushels and corn stocks at 2.594 billion bushels.

"What can you say when you have a carryover over 2.5 billion on corn and 435 million on soybeans? It's not really anything bullish to hang your hat on," said Don Roose, president of brokerage U.S. Commodities.

Most-active soybean futures on the Chicago Board of Trade were down 9 cents at $11.61-1/2 per bushel by 11:50 a.m. CST (1750 GMT), while CBOT corn eased 3-1/4 cents to $4.21 per bushel. Both markets hit their lowest levels since December 2020.

CBOT wheat dropped 16-1/2 cents to $5.69 per bushel and reached its lowest price since Nov. 28.

U.S. grains and soybeans face tough competition for export business from South America and the Black Sea region. A firm dollar, which hit three-month highs this week, also makes U.S. farm products look costlier for importers.

"Many of these markets are oversold, with managed money holding massive short positions," said Arlan Suderman, StoneX chief commodities economist. "Thus far there isn't a headline to create concern among these money managers to cause them to change their positions."

The National Oilseed Processors Association said the January U.S. soybean crush dropped by more than expected from a record high the previous month. (Reporting by Tom Polansek in Chicago, additional reporting by Gus Trompiz in Paris and Peter Hobson in Canberra; Editing by Sherry Jacob-Phillips, David Goodman and Shailesh Kuber)