GRAINS - Corn futures slide on crop-boosting forecast

* Corn futures down 3 pct on weather forecasts

* Soybeans also weaker but acreage forecast limits drop

* Light demand pressures wheat market (Updates with U.S. trade, adds quotes; changes dateline from PARIS/SINGAPORE)

CHICAGO, Aug 5 - U.S. corn futures fell 3 percent at the Chicago Board of Trade on Wednesday as forecasts for favorable weather for crop development boosted expectations of a large harvest this fall, traders said.

"There is plenty of rain in the forecast the next few days." said Vic Lespinasse of GrainAnalyst.com. "Then it is going to get hot over the weekend. All the forecasts that I have seen think that this hot spell is not going to be prolonged. Any hot spell is going to be sandwiched by beaucoup rain."

Prices for corn also were setting back from rallies during the past week that were based on expectations for hot weather disrupting crop development, Lespinasse said.

Corn futures were particularly sensitive to changes in weather forecasts as late planting in many key areas of the U.S. Corn Belt this spring left much of the crop behind its usual development pace.

Large portions of the crop were still in the vulnerable pollination phase, which determines the number of kernels on each ear of corn.

The U.S. Midwest will heat up this week, which will stir up rain storms, providing near perfect conditions for pod-filling soybeans and pollinating corn, a forecaster said Wednesday.

"This is a very optimistic forecast for the Midwest -- some rain and keep temperatures on the warmer side to improve crop development," said Mike Palmerino, agricultural meteorologist with DTN Meteorlogix.

At 12:30 p.m. CDT (1730 GMT), CBOT September corn futures were down 10-1/2 cents at $3.44 a bushel.

Soybean futures also were weaker as forecasts for a large harvest weighed on the market.

Analytical firm Informa Economics projected total U.S. soybean production of 3.322 billion bushels with an average yield of 43.5 bushels per acre, trade sources said. The firm also estimated what the U.S. Agriculture Department's upcoming crop production report would show, pegging the government's forecast for the soybean crop at 3.177 billion bushels with an average yield of 41.6 bushels per acre.

Informa pegged total corn production at 12.991 billion bushels based on a record yield of 164 bushels per acre. Its forecast for the USDA view of corn crop was 12.554 billion bushels, reflecting an average yield of 157.1 bushels per acre.

USDA will publish its monthly crop production estimate on Aug. 12.

Wheat futures also fell, pressured by poor global demand amid abundant supplies. The wheat market also was weighed down by weakness in corn futures.

"The wheat market is just reflecting that its trying to find demand," said Shawn McCambridge, analyst with Prudential Bache Commodities. "We are going to have a large crop. We are going to have an increase in ending stocks and we need to find more demand." Prices at 12:30 p.m. CDT (1730 GMT)

Pct 2008 YTD

Last Change Chg Close Pct Chg --------------------------------------------------------------- CBOT corn 3.4400 -0.1050 -3.0 4.07 -15.5 CBOT soy 11.6225 -0.0275 -0.2 9.7225 19.5 CBOT meal 362.20 -4.60 -1.3 300.5 20.5 CBOT soyoil 0.3711 -0.0034 -0.9 0.3329 11.5 CBOT wheat 5.2775 -0.1450 -2.7 6.1075 -13.6 CBOT rice 13.8000 -0.0150 -0.1 15.34 -10.0 EU wheat 134.00 -3 -2.2 137 -2.2 US crude 71.32 -0.1 -0.1 44.60 59.9 Dow Jones 9267 -54 -0.6 8776 5.6 Gold 964.00 -2.75 -0.3 878.20 9.8 Euro/dollar 1.4425 0.0033 0.2 1.3978 3.2 Dollar Index 77.5020 -0.2630 -0.3 81.1510 -4.5 Baltic Freight 3051 -108 -3.4 774 294 -------------------------------------------------------------

In U.S. dollars, front-month contracts, except EU wheat, which is in euros. CBOT wheat, corn and soybeans per bushel, rice per hundredweight, soymeal per ton and soyoil per lb.