Brett speaks for the first time in the series, saying "Oh shit" (censored) when he sees the tornado coming at him and the store while out in the parking lot.
Tornadoes are mentioned three times prior to this episode. Once in a safety meeting, tornadoes are suggested as a cover up for Marcus cutting off his thumb. Glenn later mentions he sent out a memo that no one read about how the store got an F in tornado preparedness. The third time tornadoes are mentioned is Mateo's Last Day (2017).
As mentioned above, Amy's fake name in this episode is "Dottie". Dottie is a short form of the name Dorothy. Dorothy from "The Wizard of Oz" is carried away to the land of Oz by a tornado.
All of the employees Glenn is forced to lay off return, many of them in the very next episode.