Four weeks is a dangerous sample size to use to assess a baseball season. It's just long enough for trends to develop, but not long enough for any firm conclusions to be drawn.

The National League West has featured its share of surprises during the season's first month. Some of those stories will persist throughout the year. Some will inevitably fade.

With that in mind, here's a breakdown of some the division's key storylines -- which ones are real, and which ones are not?

D-backs
What’s real: Luke Weaver’s promising start to the year. The right-hander has used his cutter more and his breaking ball less, pairing it with his fastball and signature changeup. Weaver's peripherals support his improved results. His strikeout rate is up this year and his walk rate is down.

What’s not real: The D-backs' come-from-behind magic. In 10 of their first 13 wins they trailed early in games. Teams often chalk up comebacks to factors like heart or grit. But the numbers show that coming from behind generally isn't sustainable in the long term.

Dodgers
What's real: Alex Verdugo’s arrival. He made the roster out of Spring Training and has immediately lived up to MLB Pipeline’s billing as the top prospect in the organization. He brings a youthful energy to a seasoned lineup, and if he continues to hit left-handers, he could take more at-bats away from Chris Taylor, whose struggles continue.

What's not: A team ERA in the 4's. The Dodgers haven’t had one since 2010. They’ve already had three starting pitchers on the injured list (Clayton Kershaw, Rich Hill and Hyun-Jin Ryu) and Joe Kelly has had a rough beginning to his Dodgers career. But Kershaw and Ryu are now back and Hill should be by the weekend.

Giants
What's real: The Giants' relievers have been as good as expected. The bullpen's 2.58 ERA is the lowest in the Majors. That stinginess has taken some pressure off the club's rotation and kept the Giants in games when their starters have struggled. Mark Melancon has enjoyed a particularly impressive start, working 10 2/3 scoreless innings in his first 10 appearances. He is one of two Major League relievers to have pitched at least 10 innings without allowing a run, joining the Dodgers' Dylan Floro.

What's not: The offense's .201 batting average against right-handed pitching. With a lineup that skews left-handed, the Giants were built to do damage against righties, but they've posted the second-lowest batting average in the Majors against them. That mark figures to improve as the season wears on, with left-handed bats like Brandon Belt, Brandon Crawford, Joe Panik, Steven Duggar and Gerardo Parra settling in.

Padres
What's real: Fernando Tatis Jr. is as real as it gets. The rookie shortstop is riding a 12-game hitting streak. But even if he doesn’t rake every night, he'll still find a way to impact games. Tatis boasts elite speed and defensive tools to go along with one of the best young bats in the sport. The Padres have spent the past decade searching for their long-term answer at shortstop. They've found it.

What's not: The Padres' rotation has been among the best in the Majors this season, with a 3.36 ERA. That probably isn't sustainable. The rest of the league will adapt to their young starters, plus, Chris Paddack and Matt Strahm will have their workloads limited. The San Diego starting five is clearly better than expected. But it probably isn’t this good.

Rockies
What's real: Jon Gray's detailed study of his motion, his pitches and his strategy has paid off. Last season's struggles shook the fans' faith in the 27-year-old right-hander. But in his first five starts, Gray has been much sharper, and he has displayed a better fundamental framework for his pitches.

What's not: Righty Bryan Shaw fashioned a 1.50 ERA and a .175 batting average against through his first 11 appearances. But he's walked seven and hit one batter, against just five strikeouts over 14 innings. He'll need to find the strike zone -- and induce a few more whiffs -- for his performance to hold up over time.