SEPTA spokesperson Andrew Busch said riders should brace for a difficult travel day.
"You're almost certainly going to encounter cancelations, significant delays, and at some point during the day, we're probably going to have to start shutting services down," he said.
LIVE UPDATES: Snowstorm set to hit the Philadelphia region this weekend
For many who rely on public transit, the warning is troubling.
Bajotta Richardson of Wynnefield said the disruptions would create financial and logistical challenges for getting to work on Sunday.
"It would mess me up. I'd have a hard time getting to work. It would be more Ubers. I gotta spend more money," she said.
Healthcare worker Ashley Marcus, also of Wynnefield, said the looming service cuts pose serious concerns for essential employees.
"Since I am a healthcare worker, some of us, it's not an option to come into work every day. So the fact that we have to make it through, some of us without public transportation, is gonna be extremely rough on all of us," she said.
Bus service is expected to be the first mode affected as road conditions deteriorate. Regional Rail could follow soon after.
"Regional Rail, you know, those tracks all being out and exposed, there really isn't an effective way to clear that if we're getting rapid accumulation. So at some point, we'll have to make a call, likely to pull those services back as well," Busch said.
SEPTA officials say any suspension of service will be driven by safety concerns for both riders and employees. But the agency is also focused on protecting equipment to ensure a quicker recovery once the storm passes and regular routines resume.
Marcus said some of her colleagues are already joking about extreme measures.
"A lot of my coworkers were talking about they might be skiing into work on Monday, so hopefully that's not the case," she said.
SEPTA says riders who must travel on Sunday should rely on the Broad Street Line or Market-Frankford Line, which are expected to be the most resilient during the storm.
The agency's general manager is scheduled to join the mayor and other city officials on Friday to provide an update on storm preparations.