The sound is like fighter jets. Until they are airborne. Then all is quiet as they soar toward the depths, skis in a V.

This is was what it sounded like standing next to the takeoff at the 90-meter ski jump at Lake Placid today, as the best ski jumpers in the country competed in the U.S. Ski Jumping and Nordic Combined Championships.

Yes, it’s October. And yes, they were skiing. Against a backdrop of yellow and orange foliage, 22-year-old Jessica Jerome (Park City, Utah) and 21-year-old Nick Alexander (Lebanon, N.H.) won the women’s and men’s national jumping titles. 

Wearing a sleeveless shirt, Todd Lodwick crossed the finish line on rollerskis for his 20^th national Nordic combined championship, a discipline that tests a skier’s nerve on the jumping hill and lungs in cross-country.

How can they be skiing in October? Are they jumping into water, one friend asked? Or indoors, suggested another?

Given the cold temperatures and persistent drizzle that started the day, they might as well have been jumping on snow.

Instead, they landed on plastic that’s sprayed with water. For the cross-country portion of the Nordic combined, the skiers raced a hilly 1.4-kilometer course eight times on rollerskis.

The plastic that they jump on is actually shingles of industrial-strength plastic strands that look like something you might make a hula skirt from. The sheets extend across the landing hill and are layered from the bottom of the hill up, much like you would shingle a roof. To keep them slippery, they are sprayed with water — either from an irrigation system or, as was the case today, by Mother Nature.

The jumpers assured me that the surface really does resemble snow, even if it looks like Astroturf that needs to be mowed.

At the very bottom, the plastic gives way to real grass, and the jumpers lean back hard on the tails of their skis to slow down on the grass.

As for the in-run — or jump itself — a sign on the jump’s viewing platform explains that the tracks are made from porcelain with half-cut porcelain marbles inserted in the tracks to give the jumpers a smooth surface to fly down toward the takeoff.

Skis hurtling down the porcelain at 55 mph makes the fighter-jet sound.

Surprisingly, summer ski jumping began in Lake Placid in the 1940s — long before the industrial-strength hula-skirt plastic shingles were invented. Instead, they cut ice from a nearby lake in winter and stored it in an icehouse at the top of the jump hill.

On competition day, they chipped the ice and sent it down the hill in coal chutes. Or so says a placard near the finish area. Workers shoveled it onto the hill and skiers packed it. Set up time was at least 3 to 4 hours. It makes walking the steps up the side of the 90-meter jump seem tame by comparison.

Jumping accuracy was key back then. The in-run was only 2-feet wide, and the landing hill only covered with 9-10 feet of chipped ice (compared to almost the whole landing hill like today’s plastic). Goodness knows what happened to off-balance skiers, although grass stains were probably the least of their worries.

The icehouse tradition continued until 1984 when plastic was installed at the Lake Placid jumps.

So what happens if you fall on the plastic? I only saw one guy go down. As the crowd let out a collective gasp, he slid to the bottom of the landing hill in a heap but quickly stood up, picked up his skis, and walked off. The crowd exhaled.

A bruised ego, perhaps.

Better that than grass stains.