Every summer, the quality of ad-supported cable programming seems to get better while the broadcast networks turn more and more to inexpensive reality programming.

Given that choice, viewers are inclined to go where the quality is, and that’s certainly reflected in the latest analysis of summer ratings, released yesterday by Turner Networks.

This summer, cable’s share among adults 18-49 is more than double that of broadcast, achieving its best advantage ever, despite the Big Five airing more original summer content than ever before.

Ad-supported cable networks will average a 52.4 share among 18-49s this summer, more than double the 24.2 share averaged by ABC, CBS, NBC, Fox, CW and MyNetworkTV.

Cable’s share was up 3 percent over last summer’s 51, while broadcast dipped 11 percent from last summer’s 27.2, though the consolidation of UPN and the WB into the CW accounted for a part of that dip.

Just why cable ratings are up is not hard to understand.

Cable continues to return highly acclaimed summer shows like “The Closer” and “Monk” to even stronger numbers, while parking its highest-profile new shows, like the TNT Holly Hunter drama “Saving Grace” and FX’s Glenn Close legal show “Damages,” alongside them.

Other cable series with big-name stars this summer included USA’s “The Starter Wife,” starring Debra Messing, and TBS comedies “Tyler Perry’s House of Payne” and “The Bill Engvall Show,” all of which helped their networks improve their timeslot averages in 18-49s over last year.

And summer’s second-most-watched program among total viewers, Disney’s highly anticipated “High School Musical 2” with 17.2 million, aired on cable.

Meanwhile, returning shows on broadcast like NBC’s “Last Comic Standing,” CBS’s “Big Brother” and Fox’s “So You Think You Can Dance” all dipped from last summer, while new shows like CBS’s “Pirate Master” and Fox’s “On the Lot” out-and-out bombed.

While “Pirate” and “Lot” sounded like potential hits, with big names like Mark Burnett and Steven Spielberg behind them, the broadcasters skimped on their development, and that was not lost on audiences.

Through 11 episodes, “Lot” averaged just 1.53 million viewers 18-49 while “Pirate” drew only 2.53 million and got yanked before its finale. “Closer” puts up comparable numbers though it’s available in millions fewer households.

The latest Turner numbers echo a report put out last month that predicted cable’s share of summer viewers 18-49s could double broadcast’s for the first time. The numbers have remained steady since then, with no noticeable increase or decrease for broadcast or cable.

Turner also notes that cable’s gains among total viewers are significant compared with five years ago.

Cable’s top three summer shows are pacing well ahead of 2002’s top programs. This summer, TNT’s “The Closer” (7.9 million), “Saving Grace” (5.6 million) and USA’s “Monk” (5.1 million) are all averaging more viewers than 2002’s top summer cable show, “Monk,” with 4.5 million.