CHICAGO (Reuters) -- Optimism is waning that U.S. corn yield per acre will be lofty this year since wet weather in June stunted some of the crop and now there are fears that heat and dryness in late July will cause more harm, traders and analysts said on Thursday.

That prospect, plus last week's bullish USDA crop data and outlooks for a hot and dry July are keeping the corn market on the boil, with prices soaring over 50 cents per bushel or over 15 percent to a two-month high in only one week.

"People are afraid to be short ...