Heavy rain's the main concern today for Philadelphia and its suburbs, while areas to the west and north could see snow on the ground by Thursday morning.

Predicted snow accumulations range from a coating to an inch in outer Chester, Montgomery and Bucks Counties, to two to four inches for Reading and Allentown, to perhaps six inches in the Poconos.

But along the I-95 corridor and throughout South Jersey, rain is the biggest worry.

With up to three inches possible in places, a flood advisory will be in effect from 10 a.m. to late tonight from central Delaware to central Jersey.

Small streams and the usual poorly drained low-lying streets are likeliest to flood, potentially causing traffic headaches for both the morning and afternoon commutes - and, for some spots, perhaps even into Thursday, according to the National Weather Service.

The rain also seems likely to mean a soggy holiday tree lighting service, set for 5 p.m. at JFK Plaza.

Overnight, those western and northern areas should be snow mix in, followed by a changeover to just snow.

Then colder temperatures will settle in, with highs in the 40s through the weekend, and lows around freezing mark for a few nights, followed by dips into the 20s Saturday and Sunday.

Contact staff writer Peter Mucha at 215-854-4342 or pmucha@phillynews.com.