(Rewrites with U.S. trading, adds weather outlook, changes byline, dateline; pvs MANILA/PARIS)
CHICAGO, Dec 15 (Reuters) - U.S. corn and wheat futures weakened on Friday, with ample supplies keeping a bearish tone firmly in place over the market despite signs of a pick-up in demand, traders said.
Soybean futures ticked higher, supported by bargain buying with the market on track for its second straight week of losses.
But forecasts for rain in South American growing areas limited gains in soybeans.
"A significant change in the weather pattern across South America is expected to begin this weekend and continue at least through next week," MDA Weather Services said in a note to clients. "Above normal rainfall is expected across eastern Argentina and southern Brazil ... which should lead to notable improvements in soil moisture."
However, uncertainty about the effects of the dry start to the growing season were still hanging over the market even with the improved forecast.
The Buenos Aires Grains Exchange said drought could still lead to a cut in the estimated 2017/18 soybean planting area.
"Drier conditions are expected in Argentina again from Christmas (...) meaning that the drought could quickly become an issue again," Commerzbank analysts said in a note.
The dry conditions in Argentina have also lent some support to the corn market, which has been struggling with large global supplies and strong Brazilian exports.
At 10:55 a.m. CST (1655 GMT), Chicago Board of Trade January soybean futures were up 3/4 cent at $9.68-1/2 a bushel. CBOT March corn futures were down 1 cent at $3.47-1/2 a bushel.
The U.S. Agriculture Department on Friday morning said that private exporters reported the sale of 257,000 tonnes of soybeans to China and 126,000 tonnes of soybeans to unknown destinations during the 2017/18 marketing year.
USDA also said that exporters booked sales of 134,503 tones of corn to Costa Rica.
CBOT March soft red winter wheat futures were 1-1/2 cents lower at $4.16-3/4 a bushel.
USDA said on Friday morning that private exporters reported the sale of 130,000 tonnes of soft red winter wheat to unknown destinations for delivery during the 2017/18 marketing year.
That followed news earlier in the week that U.S. exporters booked a deal to sell 120,000 tonnes of hard red winter wheat to Algeria.
The deals tempered gloom about U.S. wheat exports in the face of stiff overseas competition and record global supplies. (Reporting by Mark Weinraub in Chicago; additional reporting by Manolo Serapio Jr. in Manila and Gus Trompiz in Paris; Editing by David Evans and Grant McCool)