Oct 9 (Reuters) - Plunging temperatures and heavy snow forecast for the upper U.S. Plains from Friday to Sunday are likely to damage unharvested corn and soybean crops in parts of North Dakota, South Dakota, Minnesota, Nebraska and Iowa, meteorologists said on Wednesday.

The winter-like blast could dump up to 3 feet of snow in central and eastern North Dakota and send temperatures plunging into the 20s Fahrenheit in Nebraska, western Iowa, southwest Minnesota and the Dakotas, said Kyle Tapley, senior agricultural meteorologist with space technology company Maxar.

The forecast sent corn and soybean futures on the Chicago Board of Trade to multi-month highs this week on concerns that late-planted crops that have not yet reached maturity could be destroyed or damaged by the hard freeze.

About 14% of the U.S. corn crop and 5% of U.S. soybeans are at risk of some level of freeze damage, Tapley said.

Freeze damage can drastically reduce grain quality, leading to steep penalties for farmers selling grain to processors and elevators.

The looming harvest woes are the latest headache for U.S. farmers facing years of low crop prices, swelling grain stockpiles and declining farm incomes made worse by a trade war with China that has slashed exports.

Only 58% of U.S. corn was mature as of Oct. 6 and just 15% was harvested, according to the latest data from U.S. Department of Agriculture (USDA). North Dakota’s crop was furthest behind, with just 22% of corn mature and none harvested as of Sunday, while South Dakota’s corn was 36% mature with 2% harvested.

U.S. soybeans were only 14% harvested as of Sunday, 20 percentage points behind the average pace, USDA data showed. North Dakota and Minnesota beans were just 8% gathered while Iowa’s and South Dakota’s crop was only 5% harvested.