A Day Called X

A Day Called X is a dramatized CBS documentary film set in Portland, Oregon, in which the entire city is evacuated in anticipation of a nuclear air raid, after Soviet bombers had been detected by radar stations to the north; it details the activation of the city's civil defense protocols and leads up to the moment before the attack (the ending is left intentionally unknown). It was filmed in September 1957 and aired December 8 of that year. It was presented by Glenn Ford.

More information can be found on its Wikipedia page.