The incident happened around 1:00 a.m. at Broad Street and Susquehanna Avenue.
The thief told the store clerk that he had a shotgun that was actually an umbrella, police say.
He fled the store and no one was hurt.
Officers recovered the umbrella in a nearby Dumpster and $80 and some change were also found.
Police are going over the store surveillance and the suspect remains on the loose.