Rob Lowe, Rashida Jones

Emotions have been running high lately on NBC's best Thursday comedies. Saying goodbye to beloved characters can have that effect. Last week, Community sent Abed's playmate Troy (Donald Glover) off to sail the world with LeVar Burton, but not before staging one last epic stunt that turned Greendale into Lava World. This week, the focus shifts to a more grounded yet fictional Indiana — where, incidentally, there is an actual Greendale (I grew up there) — as Pawnee prepares a going-away bash for Chris Traeger (Rob Lowe) and Ann Perkins (Rashida Jones) on Parks and Recreation that may not be as surreal as Community's but compensates with a reservoir of genuine emotion and character-rich moments.

Plus, as Amy Poehler chirps, "Ain't no party like a Leslie Knope party!" No faux lava, but lots of love and laughs — and not a few tears, although you'll never imagine who triggers Ann's crying jag. As Chris might say, this is lit-erally the sweetest episode of the TV week, and when he presents his guy pals with thoughtful "buddy boxes," their task is to come up with a gift even nearly as meaningful. Come for April's snark, stay for Leslie's heartfelt grand gesture to the BFF she alternately describes as "Ann, you tricky minx" and "Ann, you perfect sunflower." This episode (8:30/7:30c) is so satisfying you might feel you've binged on a year's supply of Sweetums.

MORE COMEDY TONIGHT: More often than not anymore, it feels like CBS's past-its-prime Two and a Half Men is where laughter goes to die. But this week's episode (9:30/8:30c) promises something special: a return appearance by the great Carl Reiner — still sharp and witty at 91; if you doubt it, follow him on Twitter — as Evelyn's beau, now fiancé. Among the fellow legends attending his bachelor party: Tim Conway, Garry Marshall and Steve Lawrence. ... You can always tell when a sweeps month has started by the caliber of guests a show attracts. On The Big Bang Theory (8/7c, CBS), there's a definite Star Wars vibe as James Earl Jones (the voice of Darth Vader) and Princess Leia herself, Carrie Fisher, appear as Sheldon decides to organize his own alternative to Comic-Con. ... Castle's Nathan Fillion, Criminal Minds refugee Paget Brewster and the prolific Robert Patrick reveal themselves as Greendale's power brokers — you didn't actually think Dean Pelton ran things? — on Community (8/7c, NBC) as Annie plans the school's midterm dance and runs afoul of bureaucracy with the head custodian (Fillion), head of I.T. (Brewster) and head of parking (Patrick). Will heads roll by the time this is over?

THE THURSDAY GUIDE: Fox's American Idol (8/7c) wraps its auditions in Omaha before moving on to Hollywood next week. ... In the season finale of USA Network's White Collar (9/8c), Neal and Peter seek hidden treasure in New York with a criminal genius on their heels. ... With PBS's Sherlock already about to end its run this weekend, time to get back into CBS's Elementary (10:01/9:01c), with Joan Watson digging into one of Sherlock's cold cases while her mentor struggles with being a sobriety sponsor. ... Programming note: A week from now, NBC begins its prime-time Olympics coverage (getting a one-night jump on the Opening Ceremony), so Thursdays won't be back to "normal" until the end of February.

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