Friends Kyle Fullmer, of Arlington, left obscured, Ronald Copeland, of Waldorf, Md., second left, and Britney Frederick, of Hyattsville, Md., right, enjoy drinks and conversation under heaters on the patio at BarCode on Nov. 14 in Washington. (Ricky Carioti/The Washington Post)

This month’s arctic cold wave should have marked the beginning of indoor weather, when Washingtonians start limiting their exposure to quick scurries between car and lobby or office and train. So, why on a recent night, with downtown temperatures in the 30s, was Le Diplomate’s sidewalk dining area on Q Street NW packed to the planters?

Because in today’s Washington, outside is in. From the sidewalk and rooftop dining that has bloomed at eateries on H Street NE and in Shaw to the bike lanes along ever more streets, the ultimate city of insiders is bursting out of doors. Even when the weather makes one ask: Are they crazy?

Cassandra McLuckie doesn’t sound crazy (she sounds Scottish, which she is, and which might explain why she seems immune to the chill that has nearby pedestrians hunched in their overcoats). The Library of Congress researcher could have had a seat on the 70-degree side of the window separating her from the main Le Diplomate dining room. Instead, she opted for one about 30 degrees cooler on the Q Street “terrace,” where she sat happily in a fur-lined puffy coat.

“These heaters are very nice,” McLuckie explained with a shrug. “It’s noisy inside. I don’t mind the cold.”

A few feet away, a grove of upright, mushroom-shaped gas heaters cast a curtain of warm air down upon the diners. Some ate $35 steak au poivre with restaurant-supplied blankets over their knees; some were stripped to shirt sleeves. One woman was forking oysters from a bed of ice.

“I really enjoy seeing the bustle of the street,” said Hazel Wong, 43, a Nature Conservancy staffer sitting on her coat and sipping wine (a hearty malbec blend offering the right pairing with the meat-locker climate). “It’s a more socially engaged feeling out here,” said her partner, James Lockhart. “The fresh air is great.”

Also, the wait for an inside table was more than an hour.

On the street nearby, Kate Bell, 24, was locking her bike to a no-parking sign. “I’d rather ride my bike in cold weather than have to look for a parking place,” said the graduate student, who lives in a Connecticut Avenue apartment building. She was heading to meet friends on 14th Street NW and wearing a black Icebreaker riding top that is toasty enough for night biking and stylish enough for bar hopping. “I ride all year long.”

Restaurateurs, gear retailers and nature enthusiasts say demography, technology and climate are drawing Washington out in the air, even when the air has come straight from Alberta. Wrapped in high-tech fabrics and propane-fired cocoons, a region used to zipping up and hunkering down for the darkest months is carrying its buzzy millennial energy longer and longer into the winter.

As November comes to a close, bike paths remain a pedal-to-pedal parade of strobe lights. Downtown parks are filled with office workers eating food-truck lunches with gloved hands. Hiking clubs, which had been facing dwindling membership, are working to keep up with oversold weekend trips year-round.

“It feels like the adventurous, outdoorsy people are just coming out of the woodwork,” said Saul Leiken, general manager of City Bikes in Adams Morgan. “There’s definitely some kind of group effect going on.”

Like emperor penguins on the march in Antarctica? Well, not everybody is feeling so chill.

A man walking briskly past Le Diplomate’s outdoor tables took one look and shook his head.

“Not me,” he said. “Too cold.”

But the cooling trend can be good business. Leiken’s stores made most of their money during the year’s four warmest months. That “in-season” has now stretched to six months, he said, and is still growing.

BicycleSpace, a shop on Seventh Street NW, organized a “Plaid Ride” through the city this month. And the Washington Area Bicyclist Association said it is adding a December group ride to Bowie.

“Absolutely more people are riding longer in the year,” said the association’s Alex Baca. “Just go look at the bicycle racks on 18th Street in Adams Morgan. People are filling them up even in the dead of winter.”

Last year’s mild winter gave many people a chance to spend more weeks outside, Baca said, which may have helped them think of outdoors Washington as a longer-term happening.

Indeed, in recent years, there has been less of winter to endure. Fall is tending to last longer and spring is starting earlier, according to the widening gap between the first and last freeze dates.

But the youth boom is definitely at work. The 75-year-old Capital Hiking Club was facing waning participation until officers tapped a pent-up younger market using the social media site Now the club’s weekly outings to surrounding trails have become sellouts, popular with singles, among others, looking for like-minded lovers of long vistas and good outerwear.

“We hope to be around another 75 years now,” said Al Havinga, the club’s president.

The recent cold rush has some thinking about the District as a kind of Portland, Ore., on the Potomac, an eastern Seattle or San Francisco, one of those iffy-climate cities where hearty residents stay out in all weathers. Leiken has begun modeling more of his store’s rides along West Coast lines, including “Bike and Bean” (coffee roaster) and “Bike and Brew” (beer pub) tours.

But the boom in outside eating has restaurant owners looking the other direction for inspiration.

“We’re loving it. Anything that makes Washington more like Paris or Barcelona is a good thing,” said Rob Wilder, chief executive of Jose Andres’s Think Food Group. “Not a day goes by in Paris when it’s 40 degrees and rainy when there’s not somebody sitting in an outdoor cafe.”

Andres’s Jaleo in Penn Quarter helped usher in the new age of open-air dining, Wilder said, when the group asked the city for permission to add about 30 seats along its E Street NW sidewalk, something once largely forbidden by the D.C. government. Encouraged by the Downtown D.C. Business Improvement District, officials allowed a pilot program, Wilder said.

The tables are now a fixture, and all but one of the company’s seven properties has added outside seating.

“They have gotten a lot more flexible in where they allow it,” Wilder said of the District.

Restaurants are pushing the change, with pavement land grabs and rooftop colonizations offering a cheap way to expand dining rooms. (The District charges about $5 a square foot annually for sidewalk space.)

“Now, it’s a thing. Everybody has to have a rooftop or a patio,” said Ali Amarlooi, co-owner of the Biergarten Haus on H Street NE. The German pub has 600 year-round seats and an outdoor bar in its back courtyard.

Not all patrons are keen to eat outside, especially in parka weather. But managers say it’s often just a matter of getting the skeptical under heaters, which have become increasingly efficient.

“I had to ask them to turn it down,” said Jennifer Simich, a visitor from Las Vegas eating in, sorry, outside Le Diplomate. She was glad to get the table. The sidewalk seats are often the only ones available to those without a coveted reservation for the popular bistro.

This week, the restaurant added more propane-fueled heaters and enclosed part of the terrace with plastic sheets, making it comfortable for consuming escargot until spring.

Its strategy seems to be working. Even chilly nights can carry a waiting list. And terrace manager Jonathan Yeronick said the only arguments he has heard among customers about eating outside have been in the summer.

“A lot of people really don’t like the heat,” he said.