As Peter Mucha's story notes, flood watches are up all over the region, and evidently with good reason, even though the rain should be letting up for a few hours.
Montgomery County has advised the folks who live along the Schuylkill in West Norriton Township to get their duck boots ready.
It's unclear whether the rivers will go over, but it's not looking good for the usual-suspect streams in the frequent-flooder club.
Already about a third of an inch of rain has fallen since midnight at Philadelphia International Airport, and the National Weather Service warns that totals might flirt with 4 inches in some places.
The main event is expected to arrive during the evening peak commute and continue through the night.
The storm will be feeding off excellent atmospheric dynamics. As a rssult, the storm could generate powerful winds and tropical-storm force gusts.
Cold air will rush in at the very end, and some snow is almost certainly going to fall as nearby as outer Bucks, Chester, and Montgomery Counties. Some wet flakes might even show up in the city.
What is certain is that the incredibly wet year of 2011 will continue to add to its record. On Monday, precipitation at Philadelphia International Airport reached exactly 60 inches, or 5 feet, 3-plus inches more than the old record holder, 1996.