* Chicago corn drops on technical trading, rain forecasts
* Export sales news gives soybean futures a boost
* Wheat falls after hitting five-month high in previous session
CHICAGO, July 26 (Reuters) - Chicago corn and wheat futures slid on Wednesday on technical trading and news of a better-than-expected spring wheat forecast in parts of North Dakota, even as a heat wave stretched across the U.S. Midwest and part of the Mississippi Valley, traders said.
Meanwhile, soybean futures were steady to higher on the day, boosted by weakness in the U.S. dollar and news of export sales of U.S. soybeans to unknown destinations, the U.S. Agriculture Department said.
The most active wheat contract on the Chicago Board of Trade (CBOT) settled down 40-1/4 cents at $7.20 per bushel.
NATO said on Wednesday it was stepping up surveillance of the Black Sea region, as it condemned Russia's exit from a deal assuring the safe passage of ships carrying Ukrainian grain.
Corn futures followed wheat down, shedding 17 cents to settle at $5.48-1/4 a bushel. Soybean futures settled the day unchanged at $14.20 a bushel.
For much of Wednesday, traders focused on weather and potential Midwest yields.
A forecast from the National Oceanic and Atmospheric Administration's Global Forecast System Forecast System (GFS) had called for Iowa to see heat of more than 100 degrees Fahrenheit (37 degrees Celsius), said Don Roose, president of Iowa-based U.S. Commodities.
Even as a heat wave overtook part of the mid-Mississippi Valley and the Midwest - with some farmers in Missouri reporting high winds and blistering heat - traders said reports of crop-friendly rains in the northern Midwest weighed on the markets, traders said.
Adding pressure to both the wheat and corn futures, scouts of an annual U.S. crop tour late Tuesday projected that spring wheat in southern and east-central North Dakota will produce yields that are bigger than the five-year average.
"That has people thinking that if the yield in the wheat is better than we'd expected in the north, then maybe the corn and soybean yields there will be better too," Roose said. (Additional reporting by Naveen Thukral, Sybille de La Hamaide and Michael Hogan; Editing by Emma Rumney, Jonathan Oatis and Grant McCool)
