Source: Nike.

Stocks returned to their winning ways on Friday, as investors expressed renewed confidence that the Federal Reserve's future monetary policy wouldn't pose an immediate threat to the 6-year-old bull market. As of 11:10 a.m. EDT, the Dow Jones Industrials (^DJI -0.54%) were up 174 points, and the Nasdaq Composite again climbed above 5,000 in pursuit of its first record close since March 2000. Alongside the broad-based positive macroeconomic effects on the market, earnings also played a key role, with Nike (NKE -0.52%) rising almost 5% after reporting strong quarterly results last night. With Nike serving as the unofficial opening of earnings season for the Dow, now is a good time to look at how things are shaping up for the first quarter of 2015 across the market.

Source: Nike.

How Nike did it (and why the rest of the market might not)
Nike's strong fiscal third-quarter results came despite the currency headwinds that have buffeted most companies. The athletic-apparel giant's sales jumped 7% to $7.5 billion, with currency-neutral revenue rising an even faster 13%. Earnings jumped 19% to $0.89 per share, with particular strength in China and Western Europe offsetting tougher results in Japan and Eastern Europe.

Still, most investors are less optimistic about broader prospects for the coming earnings season. Projections for the first quarter are for S&P 500 earnings to fall by 4.9%, which would mark the first quarterly decline since 2012, according to FactSet. About five times as many companies have warned about negative guidance on earnings as have given positive updates, and first-quarter growth estimates have fallen by almost 9 percentage points since the beginning of the year. Revenue is also expected to fall by 2.8% among S&P 500 companies, which would be the biggest drop since 2009.

As you'd expect, energy stocks make up a large portion of the decline. Those following the sector now expect earnings to plunge more than 63% compared to last year's results, with massive cuts from the biggest integrated oil majors on down to small exploration and production companies. Materials companies have also made substantial revisions downward to their earnings projections, and while consumer discretionary stocks are still expected to see earnings growth, pessimistic trends have cut anticipated growth rates in half.

Admittedly, the calm immediately before the earnings storm is typically when maximum pessimism prevails, as companies are in a rush to pre-announce poor results but are more apt to save positive news until later. Nevertheless, the combination of the strong dollar, falling commodity prices, and global economic weakness in Europe, Japan, and China is weighing not only on market sentiment but also on actual corporate results, and a reversal of the earnings-growth trend will make the stock market's recent advance look more tenuous.

Earnings will play an increasing role in how investors perceive stocks in the weeks and months to come. Nike's news helped lift investors' spirits -- and the Dow -- today, but you should brace yourself for at least some bad news once first-quarter earnings season begins in earnest.