Expressway Mess: Blame the Fall Line?

If you live west or north of the city, normally take the Schuylkill Expressway, and you managed to drive into town this morning, congratulations.

You made it through quite a storm, a renegade that wrung out a quick 2 inches of rain and quickly engorged some of the waters coursing through parts of the region and set off flash flooding.

At 8:15 a.m., Frankford Creek was flowing at 28 cubic feet per second. At 10:45, the flow had raged to 10,100 feet per second.

Fears of a tornado in Delaware evidently did not materialize, but a small-scale storm with winds moving in circles did rotate from southwest to northeast, setting off the heavy rains.

Gary Szatkowski, the meteorologist in charge of the National Weather Service in Mount Holly, said that winds from the east up to 20 m.p.h. were measured in Mount Holly, where about an inch of rain fell.

The east wind was a tell-tell sign of the presence of a small, or "mesoscale" storm. It appears that the heaviest rains fell just to the west of the Delaware River.

Wilmington and Willow Grove both reported around 2 inches. Szatkowski said the "Fall Line" may have been a factor.

The Fall Line is an area of subtle elevation from Georgia to New England, the DMZ between the Atlantic coastal plain and the Piedmont Plateau.

The elevations are just a few hundred feet -- think of Chestnut Hill and Roxborough -- but that subtle change is enough to give an extra lift to the rising air that condenses into rain.

That's particularly true when he winds are from the east and riding up those hills.

It appears that the entire region receive a generally much-needed soaking this morning, and the inch or so measured at Philadelphia International Airport brings the month total close to the normal.

But it also appears that the rain fell hardest along the Fall Line.