April could be the cruelest month for stocks so far this year if warmer weather doesn't reverse a trend of weaker economic data.
The first big release is Friday's employment report, and the pressure is on for the March number to be stronger than February's 175,000—and even better than the consensus estimate of 195,000 nonfarm payrolls.
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"If we get 150,000—190,000, it's not momentum. It's basically the average we've had for the last year or so," said George Goncalves, head of rate strategy at Nomura. He said in order to excite markets, the number will have to top 200,000 or more.
"I think a lot of people were hoping that it will be a number that will prove it was weather that happened in Q1," he said. "If we don't get a good number, the month of April will let the air out."
In the past week, stocks told a tale of two markets—with the riskiest names hit hard and big blue chips finding buyers.
The small-cap Russell 2000 was down 3.6 percent, its worst week since June 2012. Hurt by selling in biotech and Internet shares, the was down 2.8 percent to 4,155. But the Dow was up 0.1 percent at 16,323, lifted by interest in old-line blue chips, like Exxon Mobil. The energy sector in fact was up 2.5 percent, its best weekly gain since October. The S&P 500 was down 0.5 percent at 1,857.
However, for the first quarter, the Dow is the worst performing of the major indexes, down 1.5 percent. Others are flattish, including the Nasdaq, down a half percent, and the S&P 500, the best performer, up 0.5 percent.
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Momentum stocks were sharply lower on the week. Facebook, for instance, lost nearly 11 percent and Netflix lost 12 percent. The IBB, the iShares Nasdaq biotech ETF was down 6.7 percent for the week.
Stuart Freeman, chief equity strategist at Wells Fargo Advisors, does not think the selloff in frothy names is a message about the broader market. "I don't think some of these hotter stocks pulling back is going to tell a tale for this market," he said. "We ended last year with a little bit of frenzied buying. We're working through that now."
Freeman said the market is letting off some steam, and while it could pullback, he does not expect a big correction. Freeman forecast the S&P 500 will end the year at 1,975 to 2,025, and he expects the best gains to come in the second half, after the market "chops" higher.
"We've seen a little speculation ... but we haven't seen topping type of speculation," he said. Of the selloff, "I think it's positive. That's what you want to see over time."
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Freeman said the market has a much different feel than it had at the beginning of the year.
"Utilities, health care and financials have been at the top of the market and industrials and discretionary have been at the bottom, but I do think we're seeing profit-taking in some of the better groups from last year. Some of the cyclical groups, and I also think investors, as we went through the winter and saw some of the data coming out of the cyclical economy. I think investors eased off some of the deeper cyclicals. As we come through the winter, I think we're going to see more data that looks better."
Freeman said the biggest risk for the market is if that economic data does not start to improve. "If we don't see more of pickup, even if it's not very strong ... the market could see more volatility because of that," he said.
Therefore, the always important jobs report will be very important in the coming week.
Drew Matus, senior U.S. economist at UBS, said the March jobs report should be better than February's. "I think everyone understands the weather held back a lot of industries. Since we didn't have the same kind of weather problems in March, we should get a little bit of payback," Matus said.
"I think more broadly speaking, we can tell from the claims that there hasn't been an acceleration in layoffs, and we know from everything else that the economy seems to be in an upward trajectory."
"We are at 225,000," said Dean Maki, chief U.S. economist at Barclays. Maki expects to see the unemployment rate fall to 6.6 percent from 6.7 percent.
The first quarter closes out on Monday, and it has disappointed with a string of underwhelming data. Among the latest was this week's durable goods which showed a good headline reading but a disappointing 1.3 percent decline in core orders.
Besides the U.S. nonfarm payrolls, data in the coming week includes ISM manufacturing data and car sales, two important reads Tuesday on manufacturing but also the consumer. Maki said the ISM should show improvement over February—to 54, and should show the survey bottomed in January, evidence of a weather impact.
He is also watching for stronger car sales, with a snap back in March to an annualized selling rate of 15.9 million from 15.3 million in February.
JPMorgan economists this past week trimmed their growth forecast for the first quarter to 1.5 percent, and Matus expects to see 2 percent growth. For the second quarter, Matus sees a rebound to 3.7 percent.
"We'll definitely see the data suggest that weather was the big factor early in the year, and now it has gone away. Everything is still in place for a sustained recovery, a sustained Fed tapering and rate hikes in 2015, like the Fed was telling us," Matus said.
Another big event for markets is the European Central Bank rates meeting Thursday. While not expected to take action, the ECB has made it clear it could ease monetary policy if necessary.
Vassili Serebriakov, currency strategist at BNP Paribas, said he does not expect the ECB to act yet, but he is watching European inflation data Monday just in case it misses estimates.
"I think the forecast is 0.6. If we get lower than that, markets are going to start pricing in some possibility of ECB easing. I think it's still unlikely but clearly the odds are rising. I think if we do get a weaker print by no means it's a done deal. It's still going to be a very close call," he said.
Speculation about an ECB rate cut circulated in markets this past week, but it was speculation about Chinese stimulus that helped boost stocks.
Serebriakov said he expects dollar strength against the euro and yen. "It's a function of the payrolls report on Friday, which we expect to be quite positive with a print of 210,000, and the jobless rate falling to 6.6 percent," he said.
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"We heard the optimistic Fed last week, but we need data validation so it's really now up to the U.S. data to show us this was a weather-driven soft patch and nothing more than that. There's quite a bit of weight on those numbers. It's March, and it would probably take a couple of months to get a cleaner picture," he said.
Markets are also watching developments in Ukraine. Traders have been watching the situation closely and were especially alert to developments Friday, after reports of Russian troops on the border.
Following the market close Friday, the White House announced that Russian President Vladimir Putin called President Barack Obama about the U.S. proposal for a diplomatic resolution. U.S. Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov held talks on Sunday about ways to defuse the crisis over Ukraine, with Kerry telling Moscow that progress depended on a Russian troop pullback from Ukraine's borders.
9:45 a.m.: Chicago PMI
9:55 a.m.: Fed Chair Janet Yellen at National Interagency Community Reinvestment conference
10:30 a.m.: Dallas Fed survey
Earnings: Apollo Group
8:58 a.m.: Manufacturing PMI
10:00 a.m.: ISM manufacturing
10;00 a.m.: construction spending
Earnings: Monsanto, Texas Industries
08:15 a.m.: ADP employment
10:00 a.m.: Factory orders
12:30 p.m.: Atlanta Fed President Dennis Lockhart
Earnings: RPM, Global Payments, Micron
8:30 a.m.: Jobless claims
8:30 a.m.: International trade
8:58 a.m.: Services PMI
10:00 a.m.: ISM nonmanufacturing
8:30 a.m.: Employment report
—By CNBC's Patti Domm. Reuters contributed to this report.