CBS has formalized its summer lineup, spreading scripted originals Under the Dome, Extant and Zoo across the week as the network continues its push for year-round programming. Repeats of Elementary and the Chuck Lorre comedy Mom also are expected to join the schedule, though scheduling has not yet been determined.

Pricey rookie drama Zoo, starring James Wolk and based on the best-selling book by James Patterson, will debut at 9 p.m. Tuesday, June 30. Summer staple Big Brother will have a special two-night premiere from 8-9 p.m. Wednesday, June 24, and Thursday, June 25. The Thursday edition, featuring the live eviction show, will move to its regular slot at 9 p.m. July 2. The Sunday show premieres at 8 p.m. June 28.

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Dome, based on Stephen King's novel, will move to Thursdays beginning June 25 with a two-hour premiere from 9-11 p.m. before moving to its regular slot at 10 p.m. Thursday, July 2, after Big Brother, giving Dome the network's best summer lead-in.

The third season of the drama from showrunner Neal Baer will see Emmy winner Marg Helgenberger board in an extended guest role starting in the season premiere. Details on Helgenberger's role were not immediately available, but the casting brings the CSI: Crime Scene Investigation and Intelligence alum back to the network. The series was last summer's most-watched (11.3 million viewers) and highest-rated scripted entry among adults 18-49 (2.8).

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Second-year sci-fi drama Extant, starring Halle Berry, will be back at 10 p.m. Wednesday, July 1. After shedding viewers and being moved around the schedule last summer, Extant underwent a creative shake-up ahead of season two, adding new regular Jeffrey Dean Morgan and The Walking Dead alum David Morrissey.

The network will look to expand viewership to critical darling Mom and fading drama Elementary — from Warner Bros. Television and CBS Television Studios, respectively — with the encore broadcasts. Last summer, repeats of Mom aired on TBS.

Email: Lesley.Goldberg@THR.com

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