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BlackRock pro: Bulls might need to take '2nd look'

BlackRock's Koesterich: What will concern me

The touched a fresh all-time high on Thursday, for the third session in a row. But Russ Koesterich, BlackRock global chief investment strategist, warns that if the recent spate of weakness in economic data continues much longer, bulls will need to shift their outlook on the market.

"There definitely has been a disconnect, and I think what's helped the market move higher is that investors are giving the economy a free pass, and the assumption is that it's all about the weather," Koesterich said on Thursday's episode of "Futures Now."

"You're seeing some of the weakest economic prints we've seen in quite some time. And yeah, people aren't going to worry about it, at least not yet, because they're attributing all of that to bad weather in January and February. The challenge is, [if] we get into the spring and we're still printing this low, that's when investors will take notice."

(Read more: US factory orders drop adds to slowdown concern)

In other words, if the weather turns out to be merely a convenient excuse, then that excuse can only stretch so far.

"If you get into April, and assuming March weather is close to the historical norm, then you can't blame it on the winter," Koesterich said. If "it becomes apparent that this rebound is not happening, then people are going to have to take a second look at this market."

Payrolls have been the highest-profile concern thus far, with December and January job growth numbers coming in well below expectations. But Friday's jobs report may not provide much clarity. After all, some of the raw employment data were gathered during a stormy period, meaning that weather could take the blame once again.

(Read more: Siegel: I'm a bull, but these two things worry me)

Neil Lukas | Dorling Kindersley | Getty Images

"Similar to January, there was harsh weather across much of the country during the February employment survey period. For that reason, we believe that weather is again adversely affecting the payroll data," Deutsche Bank's chief US economist, Joe LaVorgna, wrote in a Thursday note.

For Koesterich, the extent to which we can place the entirety of data weakness on the weather remains to be seen. But regardless, he wouldn't advise pulling money from equities.

"Stocks are no longer cheap, but the reality is that bonds are expensive," Koesterich said. "While I expect the returns to be a lot lower than last year, I'd still overweight stocks."

—By CNBC's Alex Rosenberg. Follow him on Twitter: @CNBCAlex.

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