Corn slumped toward the closing bell, but remained on the plus side Thursday, with other pits ending the day higher in low-volume trading focused on weather in the southern hemisphere.

At the close, March corn was 1 cent higher at $6.17 1/2 per bushel, while March wheat was 4 3/4 higher at $6.21 3/4 and January soybeans were 8 1/2 higher at $11.62 1/4, according to Barchart.com.

• Discuss today's prices in Marketing Talk
• See all the latest grain futures prices

The grains hit 1-month highs Thursday, as concerns linger about the damage hot, dry weather is doing to Brazil and Argentina's corn and soybean crops, a scenario that could limit some major competition for U.S. grain on the export market. Some estimates show as much as 2/3 of the Brazilian corn crop could be especially vulnerable to heat damage.

On top of that, this week's U.S. grain export sales numbers were higher than the trade expected, adding another bullish jolt to corn, soybeans and wheat.

• Corn export sales numbers
• Soybean export numbers
• Read more: Grains set 1-month high

Looking ahead, new outlooks show La Nina tightening its grip on the southern hemisphere, something that could increase drought risk in both South America and the U.S. Corn Belt from now through spring.