Data on small business optimism are improving but not to the point where a big rush of spending seems especially likely. And hourly wages were flat in the latest BLS jobs report, once again postponing the anticipated rise and raising questions about just how much slack remains in the labor force.
And Monday's nonmanufacturing activity report from the Institute for Supply Management offered even more confusing data. The headline number rose to 55.2 from 53.1, above the consensus of 54.0. That was good news. But the details were far less rosy.
Read More Democrats breathe sigh of relief on jobs: Should they?
The employment index dipped from 53.6 to 51.3. Pantheon Macroeconomics' Ian Shepherdson wrote in a client note that such a reading equates to a hiring pace of closer to 130,00 per month, rather than the current three-month average of 237,000.
Yellen will likely not vary in her prepared remarks from the recent Federal Open Markets Committee policy statement which said economic activity had "picked up recently" after having "slowed sharply" during the winter. And she will likely reiterate that the FOMC plans to continue to keep the Fed funds target range at effectively zero for a "considerable time" after the central bank winds up its asset purchases later this year.
The opportunity for news-making will come in the Q&A periods. Will Yellen offer any more telling detail on what a "considerable time" means? Probably not, given that markets reacted badly when she specified in her March press conference that it would be around six months. But you never know.
And how will Yellen answer Democrats eager for signals that the Fed will stay on the gas—perhaps even pausing the taper—if economic data turn uniformly soft again? And how will she deal with Republicans eager to see the central bank close down its extraordinary asset purchases as fast as possible and lean toward snuffing out any signs of inflation no matter how faint?
Read More Fed's Yellen says small bank loan growth good sign for economy
Every word Yellen says has the ability to move both markets. But the most interesting thing will be to see just how she explains the direction of an economy that seems to defy all efforts at definitive prognostication. Because if Yellen and the eggheads at the Federal Reserve can't figure it out, then maybe no one can.
—By Ben White. White is POLITICO's chief economic correspondent and a CNBC contributor. He also authors the daily tip sheet POLITICO Morning Money [politico.com/morningmoney]. Follow him on Twitter @morningmoneyben.