Why the Fed is so tough to call

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Markets have zigzagged their way through the year so far, spooked first by fears the U.S. Federal Reserve would tighten too much, then assuaged by predictions it wouldn't move rates at all.

Now, Fed forecasts run the gamut, a CNBC survey has found, begging the question: Why isn't there a consensus?

For one, the market signals have become a moving target.

"Markets are never wrong but they continue to change their minds about what the Fed will do this year," DBS Bank said in a note Wednesday, ahead of the Federal Reserve decision due later in the global day. "In January, Fed fund futures reckoned the Fed would hike 2.5 times by December. Six weeks later, all of those hikes were gone. Six weeks after that – today, that is – 1.5 hikes are back on the screen."

There's another reason there isn't much agreement on what's ahead: Many of the forecasts in the survey diverged too widely to meet easily at a median.

This chart of the results of the CNBC survey highlights the divergence of opinion.

At the dovish end of the scale, BNP Paribas doesn't expect an interest rate hike this year or next.

"For the Fed to hike rates this year, the financial markets need to recover substantially (including the risk in credit markets), while U.S. economic data need to continue to suggest that economic fundamentals remain strong," economists at BNP Paribas said in a February note. "We see a slowing in economic activity in the second half of 2016, as the benefits of lower oil prices fade (slower real income gains), global markets weighing on business investment and uncertainty remaining high."

At the other end of the spectrum, Goldman Sachs said in a note last week that it expects a hike at the June Federal Open Market Committee meeting, adding that it is "not inconceivable" that the hike might come at the April meeting instead.

"We think markets may be underestimating Fed officials' tolerance for tighter financial conditions over time," Goldman said. "We expect that financial conditions will need to tighten moderately over the next year to bring employment growth to a trend pace, which probably requires a steeper funds rate path than currently priced in the bond market."

Goldman noted that payroll employment growth rebounded in February, jobless claims have headed lower and the manufacturing sector shows signs of stabilizing.

"We see few signs that market volatility has dented U.S. growth momentum," Goldman said.

For its part, the DBS forecast is in fairly in line with Goldman's, but the Singapore-based bank thinks the June move might need to be as much as 50 basis points.

"Even with the second drop in oil prices, headline inflation is now at its highest in 15 months. More importantly for Fed policy, core inflation has accelerated sharply ," DBS noted. That means inflation may hit the Fed's 2 percent target as early as May, it said.

That means the Fed hikes may actually come too late to get ahead of rising prices, DBS said.

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—By CNBC.Com's Leslie Shaffer; Follow her on Twitter @LeslieShaffer1