A low pressure pushing east from the Ohio Valley will pick up some moisture as it crosses the Great Lakes and produce a heavy band of snowfall across parts of Pennsylvania tonight.
This will be a rain to snow scenario, with a band of very heavy snow bringing rates of 1-2" an hour for 2-5 hours, depending on location. High end snowfall amounts are expected to be 6 - 8".
Models are still trying to nail down where the narrow strip of snow will fall. We have a decent idea as to where it will be, but that will be refined throughout the day. Here is the latest 3km NAM future radar for timing.