Stocks closed out the quarter on a negative note, with a big downdraft Tuesday. The Dow's 200-point decline wiped out its gains for the quarter, and it ended the period 0.3 percent lower. The S&P 500, meanwhile, edged higher for the quarter, up 0.4 percent to 2,067.
The quarter's biggest winner was the dollar, up 9 percent, and a major loser was oil. West Texas Intermediate crude futures fell more than 10 percent in the quarter and traded lower Tuesday, as negotiations on Iran's nuclear program stretched past the deadline.
Read MoreByron Wien: Four macro myths to rethink
But the economic data are what traders are watching Wednesday, as they work to piece together a clear picture of the economy and whether the slowdown in growth is just temporary.
Jack Ablin, CIO at BMO Private Bank, said the earnings season will be critical, and the first quarter could be messy. "I think it's going to be rough. Q1 reports are going to be rough and hopefully companies will overdeliver but I think that's going to be a little turbulent, as we start to hear some of these reports. We've already heard from Sandisk, Intel, Tiffany, all warning about the strong dollar. It's possible the dollar is the new polar vortex of 2015."
For the first time in six years, analysts expect a decline in profits for S&P 500 companies.
Read MorePriced out: New housing froth discourages buyers
"I wouldn't go too far with the economic slowdown story ... the real March data isn't unveiled until Friday with the jobs report," said Chris Rupkey, chief financial economist at Bank of Tokyo-Mitsubishi. Economists have been paring back first-quarter growth forecasts and now expect a pace of about 1.4 percent.
"We'll see what March brings," Rupkey said, adding he expects 240,000 nonfarm payrolls in the government's March report Friday. "It was a really 'shoot the lights out' few months. There were 1.1 million jobs added between December and the March Fed meeting. The December and February reports were sky high. They were running 300,000."
Mark Zandi, chief economist at Moody's Analytics, said it makes sense for Friday's jobs data to come in slightly below the recent pace, in keeping with slower growth.
"Anything around 250,000 nonfarm payrolls is reasonable, given the slowing in GDP growth over the last two quarters, and you would expect job growth to moderate. ... GDP growth would suggest we would throttle back to about 250,000," he said.
The ADP data are also a bit more important this month because the cash stock and bond markets are closed Friday when the March employment report is released. Trading is open in futures markets but is expected to be thin.
Besides the ADP data, traders Wednesday will likely be focused on ISM manufacturing data and the hiring component within it. Economists expect it to slip slightly to 52.5 from 52.9, a number that shows economic expansion.
CRT Capital Treasury strategist David Ader said the ISM manufacturing data could be more important to markets Wednesday. "The sector has demonstrated weakness and now if we see that again, something's up," he said.
"It was easy to attribute (weakness) to weather but the weaker regional ISMs argue against that. Then you have the consumption figures which have a consistent story and weakness in the durable goods story," he said.
The jobs-related data, however, may carry the biggest punch this week since it has been the strongest series of economic data. Traders say if it is way different than expectations, it could be very market moving and alter expectations for the timing of Fed rate hikes.
Ader said if the Friday nonfarm payrolls are strong and there are wage gains, then traders may start speculating about the Fed moving to raise rates sooner. "The front end is going to take a nose-dive on that one. The dollar is going to be in heaven," he said. "If it's very weak, below 200,000 and maybe unemployment goes up a tick, then you say: 'Whoa, this slowdown is more than weather-related.'"
Besides economic reports, there are a few earnings including from Monsanto, Acuity Brands and UniFirst.
Read MoreQE4 may loom if US consumer stays weak: Nomura's Janjuah