For just the second time since the recession began in December 2007, the regional unemployment rate has fallen, albeit slightly, the U.S. Labor Department said today.

The rate dropped to 7.6 percent in April from 8.0 percent in March.

But keep your champagne bottles corked.

What looks on the surface like an early sign of the economy turning around is really a normal seasonal aberration, said Mark Zandi, chief economist at Moody's Economy.com in West Chester.

"I would read nothing into it, zero," Zandi said.

"Everything else says we are still losing hundreds of thousands of jobs all across the country, and more and more people are becoming unemployed," he said.

Indeed, Friday, the Labor Department will release its much-anticipated national payroll report for May. Economists forecast it will show that more than 525,000 jobs were lost in May, sending the national unemployment rate to more than 9 percent.

Even so, today's figures send out tentative shoots of hope in dry federal statistics.

Here's why: The unemployment rate is really a fraction translated into a percent. The denominator is the civilian labor force, everyone of working age who has a job or wants a job and is looking.

The numerator is the number of unemployed people. If that number stays constant or shrinks while the labor force grows, the rate of unemployment falls.

In April, the denominator swells every year as seasonal workers cocooned for the winter reemerge with the warm weather to power their buzz saws and rev up their lawn mowers.

In the part of the Philadelphia area that includes Camden, Gloucester and Burlington Counties, for example, seasonal workers helped increase the April labor force to 668,100 people, up by 3,500.

At the same time, the number of unemployed declined 2,500 to 55,400 as some of those people found work.

Divide 55,400 by 668,100 and multiply by 100 and you get the April jobless rate of 8.3 percent. That's down from March's 8.7 percent.

In Philadelphia and the four surrounding Pennsylvania counties, unemployment was 7.3 percent in April, down from 7.8 percent.

The pattern has repeated itself for at least a decade.

Even the Detroit epicenter of the collapse in the automotive industry had an April decline in the unemployment rate to 14.6 percent from 14.9 percent in March.

Contact staff writer Jane M. Von Bergen at 215-854-2769 or jvonbergen@phillynews.com.