From the crawl on any of the Sioux City, IA stations ALL are turning off the analog on the 17th.
Further investigation would be needed to figure out exactly what is happening in the market ... but one of the options is to leave the analog of at least one major station on the air with an "enhanced nightlight" program:
Ensure that at least one station that is currently providing analog service to an area within the DMA that will no longer receive analog service after February 17, 2009 will continue broadcasting an analog signal providing, at a minimum, DTV transition and emergency information, as well as local news and public affairs programming (“enhanced nightlight” service) for at least 60 days following February 17, 2009.
There is probably a station (or more) that will be "turning off" analog by ceasing normal programming. All four Sioux City network stations certified that they would follow the rules that require the "enhanced nightlight".
BTW: There is a lot of discussion on DTV Delay over in our Broadcast/HDTV ForumObama Signs DTV-Delay Bill