U.S. stocks fall ahead of Yellen speech

U.S. stocks traded mostly lower in the morning session on Wednesday, as investors awaited a key speech from U.S. Federal Reserve's Chair Janet Yellen for more clues on the timing of a next interest rate hike.

At midday, the Dow Jones Industrial Average shed 38.90 points, or 0.21 percent, to 18,508.40. The S&P 500 was down 4.42 points, or 0.20 percent, to 2,182.48. The Nasdaq Composite Index lost 5.84 points, or 0.11 percent, to 5,254.23.

Traders kept a close eye on Yellen, who is scheduled to deliver a speech Friday on the U.S. economy and monetary policy at the Economic Policy Symposium at Jackson Hole, Wyoming.

"Will the Fed raise rates on September 21? Market probability is now 28 percent, up from near zero in June, but not up much," said Chris Low, chief economist at FTN Financial, Wednesday.

However, some Fed officials' hawkish comments have strengthened market expectations that the central bank might raise interest rate later this year.

Trading volumes have been below average recently as the earnings season winds down, according to the Reuters.

"Markets are quiet in part because it's August. Stuff still happens in the summer, of course, but members of the press are on collective vacation," said Low.

U.S. stocks ended higher Tuesday, with the Nasdaq hitting a record intraday high, as Wall Street digested a batch of positive earnings reports. Enditem