JAFFREY, N.H. - For 364 days a year, the high point in Jaffrey is Mount Monadnock, 3,165 feet tall and considered the second-most-climbed mountain in the world.

But on a latter Saturday in August every year, Monadnock is eclipsed.
 
That's the day of Jaffrey's Festival of Fireworks, when the ground shakes, the sky explodes, and the town's population bursts from its usual census of about 5,400 to more than 40,000.

So how is it that such a small town could have a show that can hold a candle to the far-greater-known Fourth of July shows over the Esplanade in Boston, or over the Washington Monument in Washington, D.C.? The answer is Atlas, as in Atlas Advanced Pyrotechnics, which designs its "pyrotechnic symphonies" at a nondescript office building not too far from the center of town.

"Jaffrey is close to our heart. We weren't trying to be a destination. It started out as a small community service," said Matt Shea, an Atlas spokesman, just a couple of weeks before the 12th annual show, which is Aug. 25. "We would invite some close clients so that they could see what we could do, but we were doing it in our community."

The client list has grown over the years and so has the show, so that today it is a combination of Jaffrey's old-home week and a required stop on the fireworks fanatics' circuit. "It's designed similar to an opera, where a lot is going on, and you need to see it staged," Shea said.

If fans of the Boston or Washington shows sense some similarities at the Jaffrey show, that's not coincidence; Atlas has done the past two Boston shows, and the past five in the nation's capital. But it would be a backward perception.

"Jaffrey is the matriarch. All of our experiences we've had in designing shows, their infancy was in Jaffrey," Shea said. Jaffrey provides a different look as well, because of the surroundings. The fireworks in Boston, for example, are launched from a barge on the Charles River, and space is limited.

At the Jaffrey Airport, ground zero for the show, not only can Atlas spread out its launchers, spectators can get closer to the firing points. The effects seem to be directly overhead, and "you can feel the earth shake," said Harvey Sawyer, who operates Silver Ranch Airpark at the airport.

Sawyer said that between setup and cleanup, the runway closes for four days to accommodate the event. But Cyndy Burgess, president of the local chamber of commerce, said that for most of the volunteers who organize the show, work begins in earnest at dawn, only a couple of hours before cars start lining up outside the airport.

On first thought, it might seem silly for drivers to queue up at 8, when the gates don't open until 4 and everyone is assured a good view. But first drivers onto the property will be among the first ones out after the show, which can be a substantial difference when thousands of vehicles are waiting to exit.

For enthusiasts for whom time is worth more than money, Burgess said, the chamber offers a $100-per-car "fest pass" that guarantees entry to a special parking area as well as an early exit. The fee for just plain folk is $30 per carload. Proceeds from the event, which is the chamber's main fund-raiser, help pay for school projects and public safety improvements.

Since looking at the sky is free, it is possible not to pay anything, Burgess conceded. "But you can't see the ground displays, and you can't hear the music." People who watch from outside "sure do miss the whole atmosphere of the day," she said.

To fill the time between entry and dusk, bands provide entertainment, and there's a vendors' row selling midway fare "and a little something for the kids," Burgess said. About 6 or 7 p.m., Sawyer added, some skydivers from Pepperell, Mass., drop in. Most of the focus is on family and friends; lots of folks bring picnic dinners.

And then, finally, darkness comes and it's Atlas's time to shine, led by company president Steve Pelkey. After 30 minutes of "oohing and ahhing," as Burgess puts it, the Jaffrey extravaganza is done for another year.

Isn't it frustrating to have worked for weeks on a show - buying the fireworks from points as far-flung as China and Spain, writing the computer code that will fire them, choosing the music, laying the lines, setting the launchers - only to have it go up in smoke in just a half hour?

"Not at all," Shea said. "Part of the beauty is that it is impermanent. You can do it all over again, you can do it better." And besides, "It's amazing how permanent a good show is in some people's minds."

SIDEBAR: IF YOU GO: Jaffrey is about 75 miles from Boston in southwestern New Hampshire. Here's one way to drive there: Take Interstate 95 to Route 2 north. Take the Route 140 north exit toward Winchendon and proceed about nine miles, until 140 ends in a T at Route 12. Go left for a bit more than a mile, and turn right at the sign pointing toward Route 202 north. Stay on 202 through Ringe and into Jaffrey. From the intersection of 202 and Route 124 in the center of town, the airport is about a mile out on 124.

Cyndy Burgess, local chamber of commerce president, said cars are allowed to queue up on the side of 124 as long as they are not blocking traffic.

One hundred and fifty $100 passes are available - only in advance - by calling Burgess at 603-532-7760, or by going to Granite Bank or the Bank of New Hampshire, both in Jaffrey.

The $30-per-car pass is available from the same sources in advance for $25, but unlike the VIP passes, they do not guarantee entry to the airport. Individuals may walk in for $6.

Alcohol is prohibited, as are personal fireworks and open fires, including grills.

Information is available at www.atlaspyro.com.

For those considering making a day of it, Burgess said other activities in Jaffrey that day will include an art stroll and a rummage sale, and in addition to Monadnock, public swimming areas at Thorndike and Gilmore ponds offer access to the outdoors.