Even before Yellen's departure Feb. 3, the makeup of the Fed is changing, as are the voting members for next year, and the market expects to hear a slightly more hawkish majority.
"I really can't see it but they could surprise," said Caron, adding the Fed could acknowledge just slight growth from the tax cuts, which should not be much of a bump for the broader economy. Yellen would then have to use her final press briefing to explain a changed interest rate forecast, but Caron said he does not expect a change in forecast or any surprises from Yellen.
Seth Carpenter, chief U.S. economist at UBS, however, says he is an "outlier" and believes the Fed could up its forecast to four interest rate hikes for 2018, instead of the current three. Carpenter said it would not be a radical departure for Fed officials, since some were already willing to consider the impact of fiscal stimulus earlier this year even when there was no legislation pending before Congress.
Now that the House and Senate are working on a combined tax bill, he said Fed officials have more reason to include a small increase in GDP growth. He expects the tax bill to add a quarter percentage point to growth in each of the next several years.
"I think they could make a change to their GDP projection. They could potentially change inflation," he said. They also could change the Fed's current 2018 forecast for three hikes, presented on the "dot plot," a chart which includes each official's forecast, presented as an anonymous dot.
Michael Gapen, chief U.S. economist at Barclays, said he expects the Fed to stick with its forecast for three interest rate hikes but some officials could up their individual forecasts to four. He said concerns about sluggish inflation could keep some Fed officials with a two or three rate hike forecast but the more they lean toward fiscal stimulus, the more chance individual officials could move up to four.
Gapen said he thinks what will happen is a "little uptick in GDP" although his guess is "inflation looks the same. That should argue for just a modest adjustment in the interest rate path. I think you have to wait for tax cuts really to have passed."
Gapen did revise higher his own forecast for rate hikes from two to three for next year, based on the falling unemployment rate and the arrival of Powell. Barclays economists now expect three rate hikes — in March, June and December — taking the federal funds rate to 2 to 2.25 percent by the end of the year. The tax cuts could begin to impact economic activity in 2018, and that could lead to a faster Fed hiking cycle if economic activity picks up.
The Fed comments are unlikely to provide much new information, and Yellen is unlikely to say much at her briefing, Gapen said. "She's probably not wanting to make news because her role is getting diminished and Powell's is getting elevated. I would just look for things to be balanced."
Update: Corrects that Yellen's briefing Wednesday is expected to be her final post-meeting briefing but her final meeting is in January.