Chicago corn futures touched a two-week high on Thursday and soybean prices also advanced, with forecasts of hot and dry weather across the U.S. Midwest raising concerns about the outlook for crops in the key producing region.
Wheat was up for a third day, although gains were capped by the outlook for ample global supplies.
"Hotter U.S. weather continues to drive the market," Commonwealth Bank of Australia analyst Madeleine Donlan said.
"Forecasters say most U.S. crops are in good shape heading into next week's hotter conditions. If the heat and dryness lingers through to late July and early August though then yield potentials will be at risk."
The Chicago Board of Trade's most-active corn contract had climbed 2 percent to $3.77-1/4 a bushel by 1120 GMT after peaking at $3.80, its highest since June 30.
"Concerns about dry weather due to La Nina weather (pattern) has given upside response to prices," said Phin Ziebell, agribusiness economist, National Australia Bank.
"The real story is that a lot of corn has gone in the ground and production doesn't look terrible."
U.S. corn supplies will tighten more than expected in the coming months due to rising exports, the U.S. Department of Agriculture said in its monthly supply and demand report on Tuesday.
CBOT soybeans rose 1.1 percent to $11.17 a bushel, having climbed in the last session to $11.22 a bushel, the strongest since July 5.
Weather forecasts showed rising temperatures and decreasing rainfall in the U.S. Midwest during early August, a critical time for soybean development.
Wheat rose on spillover support from rising corn and soybean markets, although its gains were capped by plentiful global supplies and expectations that big harvests in the United States and Russia will add to the glut.
CBOT most-active wheat futures rose 1.25 percent to $4.45-1/4 a bushel, having closed up 0.3 percent on Wednesday.
"Early harvest activity has indicated Russian yields are even better than anticipated. Russia's winter wheat output is expected to be a record this year, as are Russian exports," Donlan of Commonwealth Bank of Australia said.
"U.S. wheat will face plenty of competition in the season ahead," she added.
Hot weather remains favorable for Russia's grains, the head of weather forecaster Hydrometcentre said on Wednesday, indicating that the country is still on track to harvest the largest grain crop in its post-Soviet history.
September wheat in Paris was up 0.6 percent at 162.75 euros a tonne.