Dec. 22 (Bloomberg) -- Wheat prices in Chicago rose for a sixth time in eight sessions on speculation that freezing weather will damage dormant plants in the U.S., the world's largest exporter of the grain.

Temperatures may fall to 10 degrees below zero Fahrenheit on Dec. 25 as far south as northwest Kansas, the largest wheat- producing state, said Joel Burgio, senior meteorologist for Meteorlogix LLC in Lexington, Massachusetts. Ice storms from Arkansas to Ohio could damage soft red winter wheat, he said.

``Some very cold weather this week bears watching for any threat to the winter wheat crop in the central and southern Plains and the Midwest states,'' Burgio said. ``Current indications are that any damage would be minimal.''

Wheat futures for March delivery rose 0.25 cent, or 0.1 percent, to $3.0575 a bushel at 10:56 a.m. on the Chicago Board of Trade. Prices have rallied since Dec. 2, when wheat reached a 19- month low after the government rated U.S. crop conditions as the highest since at least 1986.

About 76 percent of the crop, which is planted as late as November and goes dormant until around April, was rated good or excellent as of Nov. 28, the U.S. Department of Agriculture said Nov. 29. In 1996, 75 percent of the crop received the top marks, which had been the record.

This was the final rating until April. U.S. farmers begin harvesting the winter wheat crop around June.

Wheat prices are down 27 percent from a 19-month high of $4.24 a bushel on April 5 amid U.S. government forecasts that record global production would exceed consumption for the first time in five years. A futures contract is an obligation to buy or sell a commodity at a set price for delivery by a specific date.

Commodity funds and other large speculators increased net short positions 64 percent to 38,804 contracts as of Dec. 14, the Commodity Futures Trading Commission said Dec. 17.

``Funds have already covered some of those short positions on the recent rally,'' said Robert Lekberg, a grain analyst for Goldenberg Hehmeyer & Co. in Chicago. ``The market may have trouble moving much higher because farmers will sell more'' of this year's crop, Lekberg said.

Wheat is the fourth-biggest U.S. crop, valued at $8 billion last year, behind corn, soybeans and hay, government figures show. The U.S. is the third-biggest wheat producer behind India and China.

To contact the reporter on this story: Jeff Wilson in Chicago at jwilson29@bloomberg.net.

Last Updated: December 22, 2004 12:03 EST