Warm and dry weather in the U.S. Midwest on Wednesday will help boost corn plantings that have fallen to a record low pace, which poses a threat to production prospects, an agricultural meteorologist said.

"Today will be the best day," said Andy Karst, meteorologist for World Weather Inc. "Then showers develop tonight, with scattered showers into the weekend."

Karst said heavier rainfall would develop beginning Saturday and continue through Wednesday next week, further stalling corn seedings. "The heaviest rains will be Saturday through Monday in the west and Monday through Wednesday in the east," he said.

Drier weather late next week should allow farmers to resume plantings, he said. "It's not ideal, but not bad either. They need to get corn planted soon."

After a cold and wet spring in most of the U.S. crop belt, farmers have seeded 28 percent of their intended corn acres, up from 12 percent a week earlier but far behind the five-year average of 65 percent, the U.S. Department of Agriculture said in a weekly report on Monday.

The planting pace for corn was the slowest for this point in the year in USDA records dating back to the 1980s, lagging 1984, when farmers had seeded 29 percent of their corn.

The figure fell below the average estimate of 29 percent from analysts surveyed by Reuters ahead of the report.

For soybeans, the USDA said planting was 6 percent complete, up from 2 percent a week earlier. But the pace was the slowest for the 19th week since 1984, when soybeans were only 4 percent seeded. The five-year U.S. average is 24 percent.

U.S. corn yields are unlikely to reach their full potential this year as the slowest planting pace on record shortens the growing season, increasing risks that plants will pollinate under peak summer heat, agronomists said on Tuesday.

"We have taken some off of our yield potential," said Emerson Nafziger, extension agronomist at the University of Illinois. "Our preference is to have it in the ground by May 1."

Nafziger said that based on the last six years of the university's lab results for Illinois, corn planted after May 10 in the state, which ranks second in production of the crop, could see a yield loss of 6 percent. The yield losses increase to 12 percent after May 20 and 20 percent after May 31, he added.

Corn grown in the U.S. Midwest grain belt typically starts pollinating in July. Plant growth and yield potential can be reduced if plants are forced to devote energy to staying cool during the hottest days of summer.

Chicago Board of Trade corn futures were trading lower early on Wednesday on outlooks for improved crop planting weather. (Additional reporting by Julie Ingwersen, Michael Hirtzer, Karl Plume and Tom Polansek in Chicago; Editing by Lisa Von Ahn)