(Updates prices, analyst quotes, byline, adds details on soybean rally, changes dateline from Paris/Canberra)

CHICAGO, May 2 (Reuters) - Chicago soybeans jumped to their highest point in more than three weeks on Thursday as heavy flooding hit southern Brazil, where some farmers have yet to harvest their crops.

Meanwhile, drier weather forecasts for grain areas in southern Russia and Moscow's latest strike on Ukraine's port city of Odesa shifted attention back to Black Sea supply risks.

The July soybean contract on the Chicago Board of Trade was up 29 cents at $11.99-1/4 a bushel by 11:30 a.m. CDT (1630 GMT).

"It's the time of year where we talk about rain makes grain, but also rain makes mud," said Don Roose, president of U.S. Commodities.

Soybeans rallied with flooding affecting Brazil's Rio Grande Do Sul state where 34% of the soybean crop remains unharvested, according to state crop agency Emater.

"These very voluminous rains, with no sunny breaks to harvest (grains), always end up causing quality losses," said Adriano Gomes, a grains analyst at consultancy AgRural.

Wheat was down slightly as forecasts showed much of southern Russia receiving little rain in the coming two weeks, while parts of top U.S. wheat state Kansas were also predicted to stay dry.

A Russian ballistic missile struck a postal depot in the port city of Odesa late Wednesday, the third missile attack on the city in as many days, Ukrainian officials said.

However, market participants said the reaction to weather and war risks in the Black Sea region was being tempered by favourable early development of Russian crops and large exports.

Wheat futures had jumped to a four-month high last week, after weather concerns prompted short-covering by investors, before retreating earlier this week as rain relief was forecasted.

Solid weekly export sales data and a weak dollar also helped propel early buying for the beginning of the month, according to Karl Setzer, partner at Consus Ag Consulting.

CBOT wheat fell a cent to $5.98-1/4 a bushel and July corn added 5-3/4 cents to $4.56-1/2 a bushel. (Reporting by Renee Hickman in Chicago; Additional reporting by Gus Trompiz in Paris and Peter Hobson in Canberra; Editing by Jonathan Oatis)