GRAINS-Wheat rises; corn, soy weak ahead of three-day weekend

* Wheat gains on weather concerns, exports

* Soybean prices fall from nine-month high

* Traders square positions ahead of holiday weekend

(Updates with closing prices, adds new analyst quote) CHICAGO, April 17 (Reuters) - U.S. wheat futures firmed on Thursday, supported by short-covering, concerns that a recent cold snap in key growing areas damaged some of the crop and worries that grain shipments from the Black Sea could be disrupted by political unrest in Ukraine, traders said. Wheat also received support from better-than-expected export sales in a weekly U.S. government report. Soybeans were mixed, with old-crop contracts weakening on some mild profit taking after bigger-than-expected crush data sparked a rally that pushed prices to a nine-month high earlier in the week. New-crop soy contracts edged higher on unwinding of bull spreads. Corn prices fell through key support points on expectations that warming weather will let farmers pick up their pace of planting during the next week. Traders noted some end-of-week position squaring in all three commodities. The Chicago Board of Trade will be closed on Friday for the Good Friday holiday. Trading resumes on Sunday at 7 p.m. CDT (0000 GMT) CBOT May soft red winter wheat closed up 3-1/4 cents at $6.91-1/4 a bushel. K.C. May hard red winter wheat, which tracks the crop in the U.S. Plains, was up 3-1/2 cents at $7.58 a bushel. "The weather concerns are centered around hard wheat, and you've had a freeze event at the beginning of the week. The thing is, you don't see that damage right away," said Terry Linn of the Linn Group, a Chicago brokerage. "You need to wait until the crop gets farther along to be able to tell." The U.S. Agriculture Department said on Thursday morning that weekly export sales of wheat for the 2013/14 crop year were 438,000 tonnes, topping forecasts ranging from 50,000 to 250,000 tonnes. CBOT wheat futures rose 4.6 percent this week. CBOT soybeans for May delivery shed 4-3/4 cents to $15.14 a bushel while May corn dipped 2-3/4 cents to $4.94-3/4 a bushel. On Thursday, the May corn contract fell below its 20-day moving average for the first time since Jan. 24. For the week, soybeans rose 3.6 percent, their biggest weekly gain in 10 weeks. Corn fell 0.8 percent during the week. The USDA said that old-crop soybean export sales totaled 19,200 tonnes, within market expectations. For weeks, traders have been bracing for a report that showed large cancellations from China, the world's top buyer of the oilseed. Chinese buyers may default on a further 1.2 million tonnes of soybeans worth about $900 million being shipped from the United States and South America, to avoid incurring huge losses in a depressed local market, the country's top soy buyer said.

"It is kind of a serious issue with China defaulting instead of canceling," said Terry Roggensack, analyst with the Hightower Report in Chicago. "It is a scarier word when they default." Prices at 1:50 p.m. CDT (1850 GMT)

LAST NET PCT YTD CHG CHG CHG CBOT corn 494.75 -2.75 -0.6% 17.2% CBOT soy 1514.00 -4.75 -0.3% 15.4% CBOT meal 488.30 -2.70 -0.6% 11.6% CBOT soyoil 43.41 -0.30 -0.7% 11.8% CBOT wheat 691.25 3.25 0.5% 14.2% CBOT rice 1536.00 -2.50 -0.2% -1.0% EU wheat 217.00 -1.50 -0.7% 3.8% US crude 104.35 0.59 0.6% 6.0% Dow Jones 16,427 2 0.0% -0.9% Gold 1295.60 -6.80 -0.5% 7.5% Euro/dollar 1.3815 0.0001 0.0% 1.2% Dollar Index 79.8370 0.0340 0.0% -0.2% Baltic Freight 930 -6 -0.6% -59.2%

In U.S. cents, benchmark contracts, except EU wheat (euros) and soymeal (dollars). CBOT wheat, corn and soybeans per bushel, rice per hundredweight, soymeal per ton and soyoil per lb.

(Additional reporting by Julie Ingwersen in Chicago; Editing by Marguerita Choy and Jan Paschal)