There are dramas on television that are more ambitious technically or thematically than NBC's "Parenthood," but I honestly believe that producer Jason Katims has one of the trickiest jobs of any drama showrunner on network or cable.

Nearly every week on "Parenthood" (which begins its third season tomorrow night at 10 on NBC), Katims has feature separate storyline for each of the show's four central adult sibling characters and has to also make time for stories for at least a couple of their parents, spouses or children. The show has to balance itself pretty evenly (if not within each hour, then over the course of a season) between tear-jerking drama and light-hearted, relatable family comedy. And it has to generate dramatic stakes on a regular basis with four main characters who are, as we head into the third season, an unemployed sneaker company executive, a corporate lawyer, a small-time record producer and a bartender with aspirations of being a playwright. These are not the kinds of professions that TV shows traditionally use to drive stories and raise stakes each week (well, the lawyer is, but it's not a sexy branch of the law and the show's not much interested in her job, anyway).

In other words, there are a whole lot of moving parts to be dealt with, week in and week out. There's no way to simply put "Parenthood" on auto-pilot and let it go. There's no set formula, which even some more prestigious cable dramas (like "The Shield") have been able to lean on over the years.  There's just this family, and what's happening to various and sundry within it, and whatever can fit together within that hour to create a satisfying whole.

And because the ground the show sits on is so uncertain, it's not a surprise that it can be very uneven - not only week to week, but subplot to subplot within a given episode, with the great moments coming just often enough to compensate for the shakier ones.

There's a moment in the season premiere where one of the kids declares, "I know there's alcohol at high school parties. I watched 'Friday Night Lights.'" That's an in-joke - Katims previously ran "FNL," and the scene also features actor Michael B. Jordan, who played the East Dillon quarterback in that show's final seasons - but it's also a reminder that Katims had it easier on his older (and better) show, which always (except for the second season, which we've all agreed didn't actually happen) had the narrative engine of the football team and the incredible pressure that football placed on its characters. When you have that, you can then more easily do smaller moments where it's just a father and a daughter playing ping-pong, or two brothers drinking in the backyard, or a husband and wife having a minor argument. "Parenthood" just has to get by with its ordinary (if large and extremely close in every possible way) family, and more often than not does just fine with that.

The premiere is largely a table-setter, establishing where all the characters are since last we saw them, and what the season's early stories will be. (Minor spoilers follow.)

Peter Krause's eldest sibling Adam has been out of work long enough that he and pregnant wife Kristina (Monica Potter) are really starting to worry about money. (Also long enough for Adam to develop some strange skills to help pass the time at home.) Lauren Graham's Sarah is nervous that her daughter Amber (Mae Whitman) wants to get her own apartment, Erika Christensen's Julia is getting antsy about the adoption process, Dax Shepard's Crosby and his baby mama Jasmine (Joy Bryant) have another parenting disagreement, while Adam's daughter Haddie (Sarah Ramos) goes to a high school party despite the disapproval of recovering alcoholic boyfriend Alex (Jordan).

It is, unsurprisingly, a mixed bag. The writers have never known quite what to do with Julia and her husband Joel (Sam Jaeger), and this adoption storyline so far has her at her most unpleasant. And the Haddie storyline wobbles, as many of the show's teen stories do, between honesty and melodrama. (Again, when there's no profession to move the action, everyone's personal life has to become a much bigger mess, with more potential for tears, to compensate.)

But the Sarah/Amber story finds a nice, simple middle ground where it's a concern for Sarah, even as the show and its other characters are very aware that this is basic circle-of-life stuff. So there's tension, but it's never overdone and always in character.

The Adam storyline seems an interesting fork in the road for a show that sometimes wavers back and forth between dark drama and commercially-appealing hijinks. Without giving too much away, Adam gets two job opportunities in the course of the premiere: one a depressing, modestly-paying but stable middle manager position of the sort that lots of family men and women have been forced to take in this economy (or, worse, would be desperate to take, if only one were available), the other a riskier but far more creative and fun venture proposed by Crosby. In the real world - and/or on a more fundamentally heavy drama - Adam would take the former and suffer through it to provide for his wife and kids. On this show, though, which needs happiness and joy, and needs the siblings to interact as much as possible? Which one do you think he's going to take?

I don't need "Parenthood" to turn into a bleak kitchen sink drama. I enjoy it for its mix of tones as much as I do for the terrific performances from the cast (both the adults and the kids). But trying to be light entertainment while still keeping your characters' feet in something that you want to very strongly resemble the real world isn't easy. If Adam chooses the Crosby plan, maybe the show finds a way to make it seem real and understandable. Or maybe it just becomes an excuse to have Krause and Shepard banter for a few minutes each week, and is eventually swept away and forgotten like the period where Sarah worked with Adam and was torn between dating his boss or the cute-but-poor guy in the warehouse.

There are times when "Parenthood" can seem like a trifle and others where it's about as impressive as a broadcast network drama can get in these procedural-dominated days. But that's what happens when you're reaching as far and wide and in as many different directions as this show does. Sometimes, everything's within your grasp, while at other moments one or more things start to slip too far away. But I always applaud the effort, and most of the time the results.

Alan Sepinwall may be reached at sepinwall@hitfix.com