GRAINS-Corn, soy futures hit highest since July 12 on hot forecast

(Recasts; adds analyst quote, updates with U.S. trading; changes byline, dateline, pvs LONDON) CHICAGO, July 20 (Reuters) - U.S. corn and soybean futures rallied on Thursday to their highest respective levels in more than a week, supported by forecasts for hot weather that will stress crops in key growing regions, traders said. Both commodities were on track for their third straight day of gains. Corn led the sector, rising 2.1 percent, as much of the crop in the Midwest was entering its key pollination phase of development, when final yields are determined. "Temperatures will continue to bake the northern Plains and western Corn Belt until the weekend, with triple-digit readings expected in parts of Iowa," Farm Futures senior analyst Bryce Knorr said in a note to clients. The strength in corn pulled wheat futures higher. Traders also noted bargain buying in wheat, which has fallen for six sessions in a row, as well as support from better-than-expected export data. The benchmark Chicago Board of Trade September soft

red winter wheat contract hit a three-week low during

overnight trading. At 11:39 a.m. CDT (1639 GMT), Chicago Board of Trade corn

for December delivery were up 8-1/4 cents at $4.04-1/2 a bushel. CBOT November soybeans were 15-1/2 cents higher at

$10.28 a bushel. Both corn and soybeans peaked at their highest levels since July 12. Corn crop condition ratings declined earlier this week in top-producing states of Iowa, Illinois and Nebraska, and extended outlooks for limited rainfall were seen as threatening. "Both corn and soybean crops are now in significantly worse condition than at the same point last year, as well as below the average for the past 28 years," Commerzbank said in a research note.

CBOT September soft red winter wheat futures were up 1

cent at $5.04 a bushel. Kansas City hard red winter wheat was also higher, but MGEX spring wheat foundered in negative territory, with profit-taking a feature following its run-up to a four-year high earlier this month. The U.S. Department of Agriculture early on Thursday reported weekly wheat export sales of 669,500 tonnes, well above trade forecasts that ranged from 250,000 to 450,000 tonnes.

(Additional reporting by Colin Packham in Sydney and Nigel Hunt in London; editing by G Crosse)