Red Dawn on the Mon
The date they reference does not work out quite right for this theory, but the context of the photo sure seems to look like it went with Operation Comet which took place in Western Pennsylvania between 1949 and 1950. Whether that is the photo's actual provenance I can't say.
Operation Comet was a large exercise of Army and National Guard troops in a scenario where Soviet paratroopers invaded from the north of Pittsburgh. In the exercise the Air Force at one point 'bombs' the Emsworth Dam to slow the progress of the invaders. All while key communications were provided by local Ham radio (Young'uns: that would be the Twitter of the day) operators and flocks of carrier pigeons. Not joking about the carrier pigeons. Also, part of the exercise included preparations in case Pittsburgh was hit with an atomic weapon. I just bet it all partially inspired Troan's remarkable series that came in 1951.
Read more about the exercise in this 1949 edition of the Antiaircraft Journal (see p. 33... p. 34 gets into the carrier pigeons). Professional reading for some. Lest anyone think this was all just some fictitious war game.... in 1952 the first antiaircraft batteries would deploy to 12 sites around Pittsburgh.
I honestly only now am realizing there has been a remake of the movie Red Dawn playing in the theaters of late. Who knew? Apparently the plot of the current movie has us being invaded by North Koreans. Really?! I know the news can sometimes make it seem like it is always the very worst of times, but does anything of late really compare to the routine fears of 50 years ago. Duck and cover!