There's a chill in the air at night, which falls marginally more quickly with each passing date. Autumn isn't quite upon us in full force, not just yet, but you can sense it settling in.

The phenomenon is similar within the ecosystem of Major League Soccer. The playoff push isn't quite make-or-break, not just yet, not in a league in which fortunes turn around so rapidly. But it's getting there. The standings are becoming more rigid, and some teams have just six matches left.

With that in mind, and with the international break impacting the bulk of MLS this weekend, this feels like as good a time as any to define the most intriguing storylines of the stretch run.

1. Is Seattle yet again the team to beat in the West?

The two-time-defending conference champions still technically sit in fifth place, but the Sounders look very much like the team nobody wants to see on their side of the bracket. This year has followed a similar trajectory of the past two: a slow start that ramps up around the Fourth of July, the team raising its game with the stakes.

Having scraped 12 points from their first 15 matches, the Sounders have earned 29 from their past 11. The most recent chunk of their league-record, eight-game single-season winning streak has come against fellow contenders, including Dallas, Kansas City and Portland, which only lends further credence to their status.

At this point, this is Seattle's conference crown until somebody physically knocks it off its head.

2. Is Toronto FC toast?

Speaking of two-time-defending MLS Cup finalists, TFC is in much more dire straits. For a second there, it appeared as though the Reds, too, were turning things around, but losses to Portland and at home to LAFC have crashed them back to earth.

Toronto is nine points out of the playoffs with one game in hand over Montreal, and although it's tempting with its pedigree not to write off the champ until the last possible second, it is running out of time. The last two months are filled with formidable matchups, too, with not a single cupcake on there.

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I think TFC is done, but it'll be fascinating watching the Reds try to crawl out of the fire -- especially if they can start to build some positive momentum.

3. Can Atlanta and LAFC raise the bar for expansion clubs even higher?

Atlanta United set the new standard in 2017, breaking the league record for average and single-game attendance, finishing second in goals and earning a home playoff game. Atlanta looks set to progress even further this season, leading the Supporters' Shield standings based on points per game and with Josef Martinez already the presumptive MVP. A Shield/MLS Cup double (even a meaningful push for a double) in Year 2 would be unprecedented in MLS history.

LAFC, meanwhile, has also shattered the mold for what an expansion team is supposed to look like. Bob Bradley's men play an aggressive, attacking, fun-to-watch style and have ridden it toward the top of the West. I'm personally skeptical that its back line is going to hold up long enough for a deep run, but this club has proven me wrong before.

With Cincinnati already ramping up impressively for its 2019 debut, both on the business and player personnel side, this might be the new normal.

4. Are we due another first-time MLS Cup champion?

It has been a heady era for spreading the wealth. The past three MLS Cup champs -- Portland, Seattle, Toronto -- were all first-time winners. Not since the LA Galaxy in 2014 has one of the more "legacy" clubs lifted the trophy.

Based on the current standings, that trend might continue. None of the top three teams in the East -- Atlanta and both New York clubs -- have ever won it all, nor have either Dallas or LAFC, the squads currently in line for byes in the West.

5. Which dark horse is most likely to break through?

For a league that prides itself in top-to-bottom parity, the past two playoffs have been short of genuine shockers. Sure, Colorado looked out of place in the 2017 Western Conference final, but it was a top-two seed. Columbus' underdog run last postseason was stirring -- especially given the distraction of potential relocation -- but with Gregg Berhalter's coaching ability and having made the final in 2015, it wasn't exactly unforeseeable.

This rough-draft bracket looks more susceptible to surprises, and the upstart Union, youth-movement RSL and Wayne Rooney's D.C. United would all very much qualify as Cinderellas.