Warring weather systems battle it out and region gets soaked in the process

| Thursday, July 11, 2013, 12:01 a.m.

It was a washout waiting to happen.

Oppressive tropical air steaming Western Pennsylvania since June finally erupted, colliding on Wednesday with a cooler high-pressure system from Canada to dump near-record rain on parts of the South Hills and other Pittsburgh suburbs, forecasters said.

“The two pressure systems are going to fight it out but the Canadian one is going to win” by Thursday, said Henry Margusity, a senior meteorologist with AccuWeather.com in State College. He said Western Pennsylvanians this weekend “can actually go out and cut your grass without sloshing in the mud.”

They'll need to dry out first. Torrential rain arrived in two waves — at about 6 a.m., and then about 12 hours later.

Morning storms alone positioned the rain among the region's most intense in a decade, said state climatologist Paul Knight.

The National Weather Service reported about 2.5 inches between 6 and 9 a.m. in some South Hills neighborhoods, a burst that overwhelmed storm sewers, waterways and rush-hour traffic. Pittsburgh's single-day rainfall record for this month is 3.48 inches, on July 28, 1999, though the all-time record for the city is 5.95 inches on Sept. 17, 2004, during Hurricane Ivan, according to the weather service.

One-day rain tallies during July in Pittsburgh have topped 2.8 inches four times since 1927, weather service records show.

Water levels rose dramatically on Wednesday in part because of saturated ground, soaked by frequent storms over the past several weeks, forecasters said. Rain fell on Pittsburgh all but one or two days since June 25, according to AccuWeather.com.

“All the streams and tributaries were immediately bank-full and immediately came out of their banks,” said John Darnley, a weather service meteorologist in Moon. “There was nowhere for it to go.”

One of the worst-hit was Chartiers Creek in Carnegie, where water by midday reached 11.8 feet — up from its normal flow of 1.47 feet, Darnley said. He said nearby tributaries ran as high as 10 times normal levels.

The conditions marked a stark change from last summer, when Pittsburgh recorded just 1.96 inches of rain from June 6 to July 10, according to the New York consulting firm Weather 2000. More than 8 inches fell during the same period this summer, said company chief meteorologist Michael Schlacter, calling the discrepancy “a tale of two summers.”

Overall rainfall in Pittsburgh since June 1 is about 50 percent above average, according to AccuWeather.com. Knight left open the possibility of additional serious storms in the next month or so, “only because there's no substantive change in the way weather patterns are working right now.”

Forecasts through early next week promise sunny skies.

“It would take a while for the atmosphere to reload, to get the sort of goop you've had,” Knight said.

Staff writers Tom Fontaine and Tory N. Parrish contributed to this report. Adam Smeltz is a Trib Total Media staff writer. He can be reached at 412-380-5676 or asmeltz@tribweb.com.

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