[youtube]http://www.youtube.com/watch?v=Up1z_jpR7Cc[/youtube] Tonight, Witness: Katrina airs at 7 p.m. on the National Geographic Channel. The show collects harrowing videotape shot before, during and after Hurricane Katrina – footage that still seems impossible in an American city. At 8 p.m., HBO premieres the first two hours of Spike Lee’s follow-up to When the Levees Broke: If God is Willing and Da Creek Don’t Rise.