Economist On Philly Fed: 'Don't Take It Seriously'

The report's headline index came in at 40.8, blowing away last month's 20.7 reading and far exceeding expectations for a reading of 18.5. This reading also marked the highest level for the index since December 1993.

But some economists aren't sold on the jump.

In a note following the report, Paul Dales, senior US economist said, "We're finding it hard to take the leap in the [Philly Fed index]...seriously when other surveys have eased, when overseas demand has softened, and when the dollar has strengthened."

"We suspect the index will fall back sharply next month," Dales wrote.

Over at BNP Paribas, Derek Lindsey also noted that the strength of the Philly Fed report flies in the face of a New York Fed manufacturing report earlier this week and a flash PMI report that hit a 10-month low just minutes ahead of the Philly Fed's own release.

And at Pantheon Macroeconomics, Ian Shepherdson said the the report was, in one word, "mind-boggling."

Shepherdson added that, "We don't know what drove the change this year - and the Philly Fed press release offers no ideas - but the headline strength is reflected in surging orders and shipments, too."

And so as tends to be the case when any data, be it economic data or a company's earnings report, blows away expectations, eyebrows tend to be raised.

Dales notes that the last time the Philly Fed's report was this strong was June 2011.

But here's the big catch: a couple months later it was below zero.