A flood warning is in effect for the entire Philadelphia region, including South Jersey and Northern Delaware, as rain and even thunderstorms threaten to add to heavy rains that caused flash flooding overnight.

Several drivers reportedly needed rescuing in parts of Montgomery County early this morning.

The Perkiomen School District delayed the opening of its schools by two hours, and canceled a kindergarten circus trip.

The surprisingly vigorous rains came fast and furious overnight. At 9 a.m. the total in Doylestown was around 2.5 inches, according to the National Weather Service, and most of that fell in a three-hour period.

A check of traffic.com's incidents map, however, showed no major road closings due to flooding at 8 a.m.

The recent nor'easter caused problems on a much greater scale, causing power outages, closing some major thoroughfares, and flooding at least one town.

By 3 a.m. today, reports were coming in about many streams overflowing, including parts of the Brandwine, Pickering and French Creeks in Chester County; Perkiomen, Skippack and Towamecin Creeks in Montgomery County; and Neshaminy and Paunnacussing Creeks in Bucks County, according to the weather service.

The early flash flood warning for those counties listed towns where the threat was greatest: Spring Mount, Soudertown, Quakertown, Pottstown, Phoenixville, Perkaskie, Lansdale, Dublin, Doylestown, Collegeville and Chalfont.

The current warning mentions minor or moderate of flooding of the Brandywine Creek at Chadds Ford and moderate flooding of Neshaminy Creek at Langhorne.

At 10 a.m., thunder and lightning started rolling into Center City.

By 9:30 a.m., the official total at Philadelphia International Airport was already over a half-inch. That should be enough to float this month into second place in the April wetness derby.

The raining champ remains April 1874, with 9.74 inches. That's better than an inch more than Philadelphia has had this month, and only a deluge atop the airport rain gauge would topple that record.

That's unlikely but not out of the question, as these thunderstorms develop.

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