NEW YORK – Once a week, Amelia Heintzelman puts on two pairs of socks, two pairs of pants and two coats and ventures out to a dance rehearsal. Carrying only her phone and keys, so as not to further weight herself down, she jogs 3 ½ miles to Marsha P. Johnson State Park on the East River. There, for the next two hours, she'll be dancing outdoors.

Because she runs over, "I'm really warm by the time I get there," she said. "I try really hard to continue moving and keep that up."

Heintzelman, 27, is part of a group of dancers who gather on the waterfront for a weekly class and rehearsal. Organized by choreographer Phoebe Berglund, who leads a ballet barre warmup in white jazz sneakers and a big blue parka, the group started taking shape in August and has continued to meet regularly, even as mild days have given way to harsher weather. (For safety and style, the dancers wear matching blue satin masks embroidered with the letters PBDT, for Phoebe Berglund Dance Troupe.)

After theaters and studios shut down in the spring, leaving many dancers with nowhere to train but their living rooms, the summer and early fall brought an eruption of outdoor dance, with classes and rehearsals popping up in parks and other public spaces. When temperatures began to drop, outdoor activities tapered off. But even in the depths of winter, some artists and teachers have persisted in bringing people together to dance — in person — in the safety of the open air.

In this new landscape of outdoor dancing, ballet classes, normally held in studios equipped with barres and sprung flooring (good for jumps), have proved especially tenacious. Amateur and professional dancers don sneakers, masks and lots of layers to carry on with a familiar ritual that, for many, is essential to maintaining physical and mental health.

While Berglund's class is intended for the dancers in her troupe, others are open to anyone hardy enough to participate. Veteran ballet teacher Kat Wildish leads a class in Central Park. In a park on the Upper East Side, Dianna Warren holds a class every Saturday afternoon. And in Brooklyn, Katy Pyle — founder of Ballez, a body-positive, queer-friendly ballet company and class — leads a weekly session.

It's about togetherness

When the weather turns especially nasty, Zoom classes are offered as an alternative. But for the most part, these classes have endured without interruption, a consistency that speaks to dancers' desire to be physically present together, not cooped up in their apartments or separated by screens.

"Being with other dancers is the most rewarding thing about being a dancer," said Anna Rogovoy, 29, who began attending Pyle's outdoor class in January. She had tried taking classes online in her apartment but found that the lack of space — combined with a fear of disturbing her downstairs neighbors — was eroding her love of ballet, a form that, for her, has nothing to do with staying quiet or small.

"I don't love ballet to do little nitpicky exercises," she said. "I do all of those things so that I can explode in space and lose control and be surprising and find new boundaries in my dancing."

Until taking Pyle's class, which culminates in grand allegro (the leaping part of class) across a basketball court, she hadn't jumped in five months. When she finally did, she rejoiced. "Even just doing 16 changements" — small jumps in place — "I could have cried," she said.

To be able to dance as part of a group is a big part of the attraction.

"To actually take class with other people, it's such a huge difference," Pyle said, "in terms of relating to other people, witnessing other people, being inspired by other people, learning, socializing — so many things."

For Wildish, too, enthusiasm from students has helped to sustain her outdoor classes on top of a busy online teaching schedule.

"Everything comes back to the dancers," she said. "They are really hard-core."

Adapting to the setting

Ballet on pavement, in any weather, requires some adjustments. Wildish notes that it's harder to articulate the feet in sneakers (as opposed to soft ballet slippers), and jumping too vigorously on concrete can cause injury.

James T. Lane, 43, a Broadway performer and a regular at the Central Park class, said the weather also forces the dancers to adjust. After a heavy December snowfall, he remembers clearing out space for his feet and commencing with pliés, focused less on achieving perfection than on the spirit of communal movement.

"It's the gathering, it's the commitment, it's the community," he said. "You're not going to be jeté-ing across Central Park in the snow. You're not going to execute everything you ever hoped and dreamed. But you are going to move your body and participate in an experience unlike any other for that hour, on that Sunday, and you're going to be in it together."

Berglund, too, is undeterred by snow. Having grown up in an Oregon fishing town that she described as "cold and gray year-round," she embraces dancing with the elements.

"Ronds de jambe in the snow? Boom. You're just gliding," she said, referring to a barre exercise in which the foot traces half-circles on the ground.

On a recent blustery day, the wind gave the dancers momentum for a series of chaîné turns, as they whipped across an open stretch of pavement.

"It makes me think about special effects onstage, like fog machines, special spotlights, snow-makers, fans," Berglund said. "We've got everything. We've got all the special effects outside."