It was a cold and overcast day in April 2013, but that didn't deter 16,479 zealous women's soccer fans from walking through the turnstiles at then-Jeld-Wen Field to watch the Portland Thorns beat the Seattle Reign 2-1 in their inaugural National Women's Soccer League home opener.

In the three years since, those same passionate fans have remained dedicated to the Thorns, and the interest around the team has only grown. The club now has more than 10,500 season-ticket holders and is averaging more fans per game this year than any past season. The Thorns even drew 18,114 fans for a May game against Seattle, despite missing all of their U.S. Women's National Team stars.

This type of massive and consistent fan support is unheard of in women's club soccer. But as the sport continues to gain relevance and more fans flock to Thorns games, it raises the question: What makes Portland such a rich environment for women's soccer, and can another city replicate its success?

"It has really been one of the most satisfying things I've ever been a part of," Timbers and Thorns owner Merritt Paulson said. "The Thorns have had a massive impact on the women's professional game, in terms of really showing not just the United States, but the entire world what's possible with women's professional club soccer."

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The city of Portland first fell in love with soccer back in 1975 when the Portland Timbers joined the old North American Soccer League. The team made it all way to the finals in that inaugural season, and more than 30,000 fans packed then-Civic Stadium to watch the Timbers beat the Seattle Sounders in the playoffs. That same year, Timbers executive Don Paul announced that Portland was "Soccer City, USA."

Portland fans have always supported the women's game as well.

Starting in the 1990s, Portland legend and former Timber Clive Charles turned the University of Portland women's soccer program into a national powerhouse, helping to launch the careers of stars Tiffeny Milbrett, Shannon MacMillan and Christine Sinclair, and drawing sellout crowds to Merlo Field.

"Ever since my days at UP, soccer, especially women's soccer, has been the thing," Sinclair said. "When I played at UP, we outdrew the men's team. I think that's very unique."

Milbrett and MacMillan were both on the U.S. Women's National Team roster when Portland hosted the semifinal matchup between the USA and Germany in the 2003 FIFA Women's World Cup. When Milbrett entered the game as a substitute, the 27,623 fans inside then-PGE Park went "berserk," Fox Sports play-by-play announcer and Portland native John Strong said.

"There have been certain key individuals in key moments, in this case Clive Charles, Tiffeny Milbrett, Shannon MacMillan, and then on up the line from there, that have sort of created this constant sense in Portland of the women's game being big and important," Strong said.

Briana Brown and Angie Miller, both of Vancouver, Wash., cheer the USA Women's National Team team before the start of the 2003 Women's World Cup semifinal against Germany at PGE Park in Portland on Oct. 5, 2003. Germany won 3-0 in front of a sold-out crowd of 27,623.

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When the NWSL began play in 2013, it was already the third attempt at women's pro soccer in the United States. Two previous leagues had folded due to overspending, infrastructure problems and lack of fan support. The new league hoped to avoid those pitfalls.

Having a flagship franchise in Portland certainly helped.

With Paulson as the owner, the Thorns became the first U.S. women's pro team to have the same ownership as an MLS franchise, and being under the umbrella of the Timbers proved to be a huge asset.

"There's a huge advantage running a women's team if you control the facilities, you have some staff already in place and you know how to run a professional soccer club," Paulson said. "That's not to say it's impossible to do it as an independent operator. You definitely have some folks that are doing an admirable job, but it sure is a lot more difficult."

From the beginning, Paulson wanted the Thorns to be seen as a high-level pro organization with their own identity, but an identity equally important to the Timbers'.

Outside Providence Park, the Thorns' logo is just as prominent as the Timbers'. The club markets the team to fans of all ages, rather than treating it like a niche product for young girls and families. And each year, the club has tried to improve the quality of the team while bringing in some of the world's top players.

Not only did the Thorns benefit from having a built-in infrastructure, high-quality, professional stadium and experienced staff, but they also had the advantage of a built-in fan base from the beginning.

Shortly after Portland was granted an NWSL franchise, more than 50 fans -- most of them avid Timbers supporters and members of the Timbers Army -- got together to lay the groundwork for a dedicated supporters group for the Thorns.

The group was not only passionate about women's soccer, but keenly understood what it would take to build a unique and exuberant supporters culture.

On that first night, the group split into sections to talk about capos, developing chants, creating tifos, and all the other things that would go into building a distinctive atmosphere at Thorns games. The Rose City Riveters were born.

"This was a group of people that were really passionate about having a women's team," said Sunday White, who has been a capo for the Rose City Riveters since 2013. "We wanted to show these women our passion and excitement and give them the same energy we give in the Timbers Army for the Timbers. We were able to take our experience from the Timbers Army and transition that to the Thorns."

Portland Thorns fans showed up in droves for the franchise's inaugural home game at then-Jeld-Wen Field on April 21, 2013.

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Portland's success has prompted two other MLS organizations to start women's teams in the NWSL.

The Houston Dash joined the league in 2014 and immediately became the second-most supported franchise. The Orlando Pride joined this season and broke Portland's attendance record in their home opener, drawing 23,403 fans to a game against Houston at the Citrus Bowl.

But neither team has come close to consistently drawing numbers that rival Portland.

Houston averaged just 6,413 fans per game in 2015, far under the 15,639 that the Thorns averaged. Orlando's attendance numbers have dropped to less than 8,000 per game since that home opener.

It's hard to pinpoint exactly what has made the Thorns so uniquely successful. Portland's history with soccer certainly plays a factor, as does having a market that's not oversaturated with professional sports. But the way many Portland fans grasp on to the Timbers and Thorns as part of their lifestyle is also noteworthy, said Hunter Shobe, an associate professor of geography at Portland State University who has studied soccer culture in the Northwest.

"There's a chemistry of things that have happened in Portland that have created this soccer culture," Shobe said. "This is a phenomenon that could happen in other places, but it would have to happen in its own way. You can't just study Portland and replicate it."

If any team has the chance to match Portland's attendance numbers in the long-term, it might be Orlando.

Like Portland, Orlando is known for its vibrant and dedicated soccer culture, and the city doesn't have a surplus of pro sports. For now, Orlando is making due playing in an oversized football stadium, but will start competing in a soccer-specific stadium next year, which could make the game-day experience more desirable for Pride fans.

"I think with anything, the success of this team is going to grow over time," said Teresa Tatlonghari, Vice President of Marketing for Orlando City SC and the Orlando Pride. "This market has been so receptive to the Pride. Especially with the new stadium opening next year, that's going to be another exciting factor and it's going to make the game-day experience so much better."

For now, the Thorns stand alone with their fan support, but there are plenty of indications that women's soccer is on the rise in this country.

The U.S. Women's National Team gave the sport a huge boost last summer by winning the 2015 FIFA Women's World Cup. Their victory over Japan in the final became the most-watched soccer match -- men's or women's -- in U.S. history. And almost every team in the NWSL saw its attendance numbers rise after the World Cup.

Ultimately, Paulson said it is not all about attendance numbers. He just wants to see other NWSL clubs growing into relevant brands and becoming economically sustainable products -- and he believes that's already beginning to happen.

"With the growth of women's soccer, it has been the perfect storm recently," Paulson said. "I think the time is ripe and I think people's interest has been piqued. It doesn't feel like this is just a bounce that came with the success of the World Cup. I think there's something bigger happening."

-- Jamie Goldberg | jgoldberg@oregonian.com

503-853-3761 | @jamiebgoldberg