GRAINS-Wheat, corn, soy tumble on better U.S. weather, technicals

* Wheat on pace for biggest two-day percentage drop since 2016

* Corn, soy futures down 2-3 pct

* Weather seen less hot next week in U.S. Midwest (Updates prices, adds analyst comments; changes byline, dateline, previously PARIS/SYDNEY)

CHICAGO, July 13 (Reuters) - U.S. grain and soy futures plummeted on Thursday, with wheat easing as much as 5 percent in a technical selloff amid outlooks for slightly cooler temperatures and chances for rain next week in Midwestern growing regions, traders and analysts said.

Wheat, corn and soybeans extended steep losses from Wednesday that followed a U.S. Department of Agriculture monthly supply and demand report showing relatively robust global stockpiles of the crops.

"The fact the U.S. numbers were more bearish than expected took some of the heat out of CBOT wheat markets," said Angus Thornton, commodity analyst at Profarmer.

Global benchmark Chicago Board of Trade September wheat fell 24 cents per bushel to a two-week low of $5.13 per bushel at 11:41 a.m. CDT (1641 GMT). The contract declined from a 13-month high reached July 5 and was on pace for its biggest two-day percent drop since April 2016.

MGEX September spring wheat futures were off 28 cents to $7.54-3/4 per bushel.

The USDA's July report increased U.S. winter wheat production while reducing projected output of spring wheat - the variety that has been hit by drought and heat in the northern Plains - by less than expected.

The USDA also raised its forecasts of end-2017/18 U.S. corn stocks to 2.325 billion bushels, up from 2.110 billion in June and above an average of analyst estimates of 2.181 billion.

CBOT September corn futures were down 12-1/2 cents to a nearly two-week low of $3.73 per bushel and CBOT August soybeans were down 35 cents to $9.85-3/4 per bushel, lowest since July 7.

Much of the U.S. corn crop goes through its yield-determining pollination phase in July. Forecasts for slightly less heat next week were seen as beneficial for the developing corn and soybean crops.

"There's a little bit of a shift in weather patterns," said EFG Group analyst Tom Fritz. "Next week, it's going to be hot, but maybe not as hot as we thought. Toward the end of next week, we might have some moisture leaking in."

U.S. grain and soy supplies also were falling out of favor in global export markets due to cheaper South America supplies. The USDA earlier showed U.S. corn and wheat sales generally in line with the low expectations set by analysts while soybean export sales were slightly above expectations. (Additional reporting by Colin Packham in Sydney and Gus Trompiz in Paris; Editing by Tom Brown)