An annual tradition on CBS for decades, the 2013 NCAA Basketball Tournament (11 a.m.), or “March Madness,” begins today in earnest. In addition to CBS, games will also be airing throughout the day on TBS, TNT and Tru TV.

There were years when the arrival of prime-time basketball offered the network its only chance to reach a wide audience. But that has not been the case for some time now, since CBS became the highest-rated network. But basketball still might reach younger male viewers who aren’t exactly glued to “NCIS.”

In addition to CBS’ NCAA competition on prime time, the cable network CBS Sports has scheduled more than 90 hours of live coverage and encore programming during the 2013 tournament. “NCAA March Madness 360” (1:30 p.m. to midnight) offers continuing highlights of the day’s action.

• While popular, college basketball coverage hardly eclipses the ratings of other sports programming, like NFL football. And there is interesting counterprogramming for nonsports fans.

”Glee” (8 p.m., Fox) has long played up the distinctions and similarities between the arts crowd and sports cliques. Tonight, the teen performers dive deep into their guilty pleasure songbook to warble some groan-worthy tunes.

A form of musical chairs unfolds as fans vote a second finalist off “American Idol” (7 p.m., Fox).

And far from the locker room, “The Vampire Diaries” (7 p.m., CW) flashes back to Damon’s decadent lifestyle in New York during the heyday of disco in the 1970s.

• As if the weather did not seem apocalyptic enough, the Weather Channel explores grim, “what if” scenarios on “Forecasting the End” (8 p.m.). Tonight, experts contemplate the arrival of a rogue planet in our solar system large enough to affect the Earth’s orbital path.

Tonight’s other highlights

• Winter X Games (6 p.m., ESPN) resume in Tignes, France.

• The gang goes on a class trip on “Community” (7 p.m., NBC).

• Families enter a parallel domestic universe on “Wife Swap” (7 p.m., ABC).

• Emily tries to help Skip buckle down in order to graduate on “1600 Penn” (7:30 p.m., NBC).

• Meredith fears for her unborn child on “Grey’s Anatomy” (8 p.m., ABC).