Beware the Ides of April.

As that well known Roman risk taker Julius Caesar found out many quarters ago, living up to expectations can be a tough job. And the crowd can take it out of your hide whether you do or don’t.

All that applies to the upcoming earnings reporting season, of course. Alcoa (AA), which dipped yesterday, April 5, on a downgrade from Morgan Stanley, tips off reporting season on April 12. Intel (INTC) follows with earnings on April 13. YUM Brands (YUM) reports on April 14; Google (GOOG) on April 15; and then Bank of America (BAC) starts off a run of bank financial earnings on April 16.

Companies are likely to report good earnings growth for the quarter that ended on March 31. The economy has indeed rebounded from recession and comparisons are still working in companies’ favor. It won’t be hard to turn in a performance that beats that of the first quarter of 2009. In the first quarter of 2009 real U.S GDP dropped at an annual rate of 6.4%.

 In the fourth quarter of that year real GDP grew at an annual rate of 5.6%. Economists are expecting that growth will slow from that pace to something like an annual 2% to 3% rate in the first quarter. But that will still be more than enough to beat the huge drop in economic growth—and corporate profits—in the first quarter of 2009. (The Department of Commerce is scheduled to release first quarter GDP numbers before the stock market opens on April 30.)

But there are three good reasons to expect that the shares of many companies reporting good earnings will still sell off on the news.

First, stock prices have been in rally mode since the February 8 low. The Standard & Poor’s 500 Stock Index is up 12.3% since that low as of the April 5 close. That climb anticipates a lot of the good earnings news that companies will deliver in the next few weeks. Investors, having already bid up stocks, are likely to ask, Is that all you’ve got for me? And sell the shares of companies that don’t deliver not just good earnings, or an earnings surprise, but higher guidance for the second quarter. That’s a lot to ask.

Second, stocks in some of the best performing sectors, such as technology, are entering the traditional summer selling season. Almost every year investors in technology prove that the saying Buy on AEA in November and go away in May. (The American Electronics Association holds its big technology conference for Wall Street and the press in November.) Technology stocks have been a leader in the rally off the February 8 low and the temptation will be to take some money off the table as the calendar heads toward May.

And third, global stock markets have spent 2010 swinging between enthusiasm over growth prospects—especially in China—driving demand for commodities and manufactured goods to fear that growth—especially in China—is so hot that governments will be forced to take measures to slow their economies. Right now the market is in the enthusiasm over growth stage. That’s why commodity and manufacturing stocks, engine maker Cummins (CMI) or Dow Chemical (DOW), for example, have outperformed safe consumer and healthcare stocks recently. But with economists increasingly warning that China’s first quarter GDP growth could be a scary 10% or better, I would say that the pendulum is scheduled to swing back.  

Should make for an interesting—if not terribly profitable–month.