Then the threat rises, depending on the timing of front coming through from the Great Lakes, and possibly spawning lines of thunderstorms, according to meteorologist Valerie Meola of the weather service's Mount Holly office.
"It might not even make its way through our area until Sunday night or Monday," she said.
An online forecast discussion predicts: "The precipitation will become heavier and more widespread as we get into the frontal zone later Sunday through Monday."
As of this morning, the highest odds for rain in the city and at the Shore were 40 percent for Sunday night. It's 30 percent for Monday.
But that could change.
"There's still so much uncertainty with how much may fall and where," Meola said.
The system seems like a slow-poke, which means it could show up late then linger, letting precipitation totals climb, Meola said.
"A lot of times these fronts move through rather quickly, but this one's going to take its sweet time," she said.
As usual with thunderstorms, some places could get an inch or more of rain, while others get little.
Friday the picture should become clearer, she said.
Tuesday, fair weather is expected to return.
For more on the forecast, go to http://go.philly.com/weather.
Contact staff writer Peter Mucha at 215-854-4342 or email@example.com.