* Wheat rises after reaching 15-week low on bargain buying, positioning ahead of USDA report

* U.S. harvest pressure, Russia rains weigh on wheat futures

* U.S. Midwest weather key for direction in corn, beans

CHICAGO, June 26 (Reuters) -

Chicago Board of Trade (CBOT) wheat bounced back on Wednesday, with the market recovering from a more than two-month low with bargain buying and positioning ahead of the U.S. Department of Agriculture's acreage report.

The most-active corn and soybean contracts edged down as the market assessed the impact of floods on crops in the U.S. Midwest.

Analysts said traders were positioning ahead of the release of USDA data due Friday.

"I think you've got a little bit of short covering, but also sort of a reluctance to sell terribly aggressively in front of one the biggest USDA reports of the year on Friday," said Ted Seifried, chief market strategist at the Zaner Group.

Bill Lapp, founder and president of Advanced Economic Solutions also said fund positioning ahead of the report was primarily responsible for the Wednesday's price movements.

Meanwhile traders continued to weigh the impacts of flooding and extreme heat in top corn and soybean growing areas of the central U.S., and the degree to which excess moisture might destroy crops or mitigate the effects of the heatwave.

The most-active wheat contract on the Chicago Board of Trade added 1/2 cent to $5.61 a bushel, as of 12:21 P.M. CDT (1715 GMT).

Corn fell 4 cents to $4.39 a bushel and soybeans lost 2-3/4 at $11.08-3/4 a bushel.

The wheat market recovered after tumbling earlier in the week as a rapidly advancing U.S. harvest showed good yields and weather stabilized in Russia and the Black Sea.

Statistics Canada is also scheduled to release its estimates of Canadian crop plantings on Thursday.

A heatwave forecast to spread throughout Europe this week is set to take a heavy toll on summer crops in the southeast, but it is good news for farmers on the other side of the region after prolonged rains flooded fields and hampered plants' growth, analysts said. (Reporting by Renee Hickman in Chicago; Additional reporting by Naveen Thukral and Sybille de La Hamaide; Editing by Aurora Ellis)