The Dow Jones Industrial Average closed at 22859.60 on Thursday with a loss of -464.06 points or -1.99%.
The benchmark S&P 500 index has slumped 10.6 percent this month and is nearly 16 percent below the peak it reached in late September.
Yardeni said Fed officials need to get on the same page.
Powell said at a news conference Wednesday that the economy remains "healthy" and "solid" and that he did not see any reason to sharply change the Fed's path of gradually pulling back support for it.
"The bond market has been telling us something for about a year, and that is there's not going to be much inflation and there's not going to be a sustained surge in economic growth", said Wren, of Wells Fargo. The bond-buying has the effect of sending long-term bond yields lower, which reduces interest rates on mortgages and other kinds of long-term loans.
"We are listening. There are risks to that outlook that maybe the economy will slow further", Williams told Steve Liesman on CNBC's "Squawk on the Street". President Trump has threatened not to sign a Senate appropriations bill averting shutdown unless Congress agrees to $5 billion in extra funds for the USA southern border wall.
The Nasdaq is the first of the three major US stock indexes to cross that threshold, with its drop in less than four months the latest sign that the bull market that began during the financial crisis a decade ago could be nearly done.
The Dow fell 518 points, or 2.2 percent to 22,718.
With December 21's losses, the Nasdaq has fallen almost 22 percent from its August 29 high.
Several other key indexes in recent days have confirmed they were in bear markets, among which are the Russell 2000 small-cap index .RUT and the Dow Jones transportation average .DJT . The yield on the 2-year Treasury note fell to 2.62 percent from 2.65 percent.
In the cash market, the benchmark S&P 500 Index settled at 2467.42, down 39.54 or -1.58%. Those worries are reinforced by a 30 per cent-plus decline in world oil prices since October. The Russell 2000 index of smaller-company stocks lost 33.92 points, or 2.6 percent, 1,292.09.
Oil prices continued to retreat.
Stocks sank almost 500 points Thursday on the news that President Donald Trump would not sign the spending bill that would avert a partial government shutdown Friday night. The tech-heavy Nasdaq composite slipped 27 points, or 0.4 percent, to 6,611.
As investors adjusted to the prospect of a weaker economy and lower long-term interest rates, the dollar fell to ¥110.90 from ¥112.36.
The British pound rose to $1.2671 from $1.2621. Copper lost 0.8 percent to $2.67 a pound.
Walgreens fell 2.8 percent and Conagra, a giant food maker, fell 7.4 percent.
Oil prices, which slid just over 4 percent on Thursday, tumbled to their lowest since the third quarter of 2017. Natural gas gave up 3.8 percent to $3.58 per 1,000 cubic feet.