The economy last grew that much in the 3rd quarter of 2013, when it registered 4.1 percent growth.
UBS entered the 4 percent growth club with a 0.9-percentage-point rise in its forecast to 4.6 percent, topping the group. The bank cited the diminishing declines in government spending, greater availability of credit and pent-up household demand as reasons for its economic upgrade. Key to the UBS forecast is a surge in capital spending to 15 percent at an annual rate in the second quarter from minus 6 percent in the first quarter. The bank sees a similar rebound in housing and forecasts a sharp decline in the unemployment rate this year to 5.5 percent from the current level of 6.3 percent.
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The forecasts follow a surprisingly anemic government report last week that the U.S. economy grew just 0.1 percent in the first quarter. Subsequent data has prompted economists to mark down that number to minus 0.1 percent, according to the CNBC Rapid Update average of tracking forecasts.
Some economists have chosen not to mark up second-quarter growth because they believe the first quarter will be revised upward. One of the big questions is consumer spending, which was a bright spot in the first quarter, rising by 3 percent at an annual rate. Many believed that the increase was driven by the Affordable Care Act, which might show up again in the second quarter.
"The big point of confusion here is (consumer spending) and what exactly is going on as it relates to the Affordable Care Act,'' said Thomas Simons, an economist at Jefferies. "There just isn't enough clarity on this point ... and it is going to be a big swing factor."
Still, even those who didn't mark up their surveys are worried they are too low. "Our 3.0 percent consumption forecast for Q2 14 should be easy to achieve, and we see upside risks," wrote Barclays.
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The upgrades to 4 percent aren't a big deal by themselves. Indeed, if the first quarter remains unchanged, or is even revised up slightly, average growth in the first half would come in at right around the 2.25 percent average that has prevailed since economic recovery began in 2009. However, most economists stuck to their forecasts for 3 percent growth for the remainder of the year, suggesting the second quarter acceleration will represent both a snapback from the weak first quarter and a higher gear for the quarter ahead.
Many of the risks cited in the Wall Street forecasts surround developments overseas, with some concerned about tensions in Ukraine and growth in China and other emerging markets. But there are also worries that capital spending may not revive or that housing woes don't reverse.
—By CNBC's Steve Liesman.