An April that rose to historic depths

With surprise deluges that turned waterways chocolate-brown, set off widespread flash-flooding and made a mess of yesterday's morning commute, April 2007 reached a miserable milestone.

Officially, the 1.6 inches of rain measured at Philadelphia International Airport pushed the monthly rainfall total past 9 inches.

The last time that happened, in 1874, Ulysses S. Grant was president, and he had just ordered the government to create a nationwide weather service. While no serious flooding, injuries or evacuations were reported yesterday, both the Brandywine Creek, in Chester County, and the Neshaminy, in Bucks, spilled their banks.

The rains also prompted two Bucks towns, New Britain and Solebury, to declare states of emergency and forced the closing of at least 20 roads, according to the Bucks County Emergency Operations Center. Three others were closed in Chester County.

Perhaps because of a quirk of geology, the rains were heaviest in a band north and west of the city, with just over 4 inches reported in Doylestown.

The forecast had called for maybe an inch or so.

The amounts were "a little on the surprising side," acknowledged Gary Szatkowski, the meteorologist in charge of the National Weather Service office in Mount Holly. He said the weather service was geared up for strong thunderstorms, not widespread heavy rain.

Around here, the storm - a remnant of the one that spawned killer tornados in Mexico and western Texas - appeared to focus its attention on an area from the Chester County-Maryland border to northwestern New Jersey.

"It's like someone took a ruler and a pencil, said Szatkowski. "A thick pencil . . .

"Why the convection became entrained where it did, I really can't say."

He noted, however, that the areas that were heaviest hit were right along the so-called Fall Line.

That's an imaginary line, just a few miles wide, that extends all the way from the Carolinas to New England. That's where the Atlantic Coastal plain begins to give way to the Appalachians.

It is well established that precipitation along the Fall Line on average is higher than that measured to the south, at the airport.

The slight increase in elevation of only a few hundred feet along the Fall Line can be enough to give extra lift to the rising air that cools and condenses and falls back as rain, weather experts say. That's especially true when the winds are from the east, as they were during the heaviest downpours early yesterday.

Today brings only an outside chance of showers, so it appears that the 1874 record of 9.76 inches will stand. Through 5 p.m. yesterday, the April 2007 total stood at 9.04.

And we can say one thing positive about a month that has so far yielded just three clear days: Tuesday is May 1.