Intelligencer Journal, Blaine Shahan, Associated Press
Six people are stranded on the back of a pickup truck awaiting rescue as flood waters rise around them, Wednesday, Sept. 7, 2011 in Mount Joy, Pa. The rainy aftermath of Tropical Storm Lee set off flash flooding across a wide swath of Pennsylvania on Wednesday, snarling traffic amid closed-off roads and forcing evacuation of some low-lying areas. State officials braced for potentially worse problems along the swelling Susquehanna River and several creeks and streams.

HARRISBURG, Pa. — The rainy aftermath of Tropical Storm Lee set off flash flooding across a wide swath of Pennsylvania, closing roads, inundating homes and forcing evacuations as waters were expected to rise to near-record levels.

Gov. Tom Corbett said the Susquehanna River — which was still rising Wednesday night in communities from Harrisburg to Towanda — is projected to crest only slightly below the historic marks recorded during Hurricane Agnes in 1972.

Corbett urged residents to take immediate steps to avoid becoming victims of the moderate to major flooding that he said is inevitable along the river basin through the weekend.

"This is not a time to panic. This is a time to prepare," Corbett said at a Wednesday night news conference at the Pennsylvania Emergency Management Agency headquarters on the outskirts of the capital.

Five-hundred Pennsylvania National Guard troops were being deployed and state emergency management chief Glenn Cannon said he may recommend activating more troops, depending on the extent of the flooding.

Much of central and northeastern Pennsylvania was pounded by rain on Wednesday, with final storm totals predicted to be five to 10 inches. Damage included a mudslide in Lancaster County and two zoo animals in Hershey that had to be euthanized after being caught in rising floodwaters.

Several school districts in flood-prone areas dismissed students early on Wednesday and some districts along the Susquehanna have canceled classes on Thursday.

The Department of Conservation and Natural Resources warned property owners to watch steep slopes and urged motorists to use caution, noting the deluge has increased the danger of landslides.

The road closures involved most of the interstate highways, including Interstate 83 at York, and a much larger number of state highways and local roads. State transportation officials urged motorists to limit travel to the most essential trips and to stay off the roads if possible.

The Pennsylvania Emergency Management Agency said it was closely monitoring the Susquehanna, Juniata and Delaware rivers for potential flooding, said spokesman Corey Angell.

In Harrisburg, the state capital, Mayor Linda Thompson declared a citywide state of emergency. The Federal Flood Forecasting Center predicted the Susquehanna River would reach the flood stage of 17 feet early Thursday and would crest at 26.2 feet early Saturday morning.

Near Hershey, the National Weather Service said the Swatara Creek was set to reach a record 20 feet by Thursday morning, surpassing the 16.1 foot record it set in June 2006.

ZooAmerica, part of the Hershey entertainment resort complex, closed early so that staff could begin moving animals to higher ground, spokeswoman Mindy Bianca said.

But water in the bison enclosure rose from inches to feet in about 15 minutes, trapping two animals, Bianca said. They could not be rescued in time and were euthanized.

"This was a really tough choice that our zoo staff had to make," Bianca said.

States of emergency were declared in at least half a dozen counties, as well as smaller cities and towns.

State Sen. Vincent Hughes, minority chair of appropriations committee, said the amount of rain was great.

"I'm glad we got into State College, I swam up ... flew into Harrisburg then did the backstroke," Hughes, D-Philadelphia, joked at a hearing on higher education funding on the Penn State campus in State College.

In Wilkes-Barre, officials issued an evacuation order affecting about 3,000 residents around 1:30 a.m. Wednesday, after the Solomon Creek rose from 4 to 11 feet in three hours. It was rescinded around 11 a.m. after the water began to subside.

But the rising Susquehanna River led emergency officials to order evacuations Wednesday night in several other Luzerne County communities, including West Nanticoke, Plymouth and Shickshinny.

The river is projected to crest in Wilkes-Barre at 38.5 feet early Friday, about 2 feet shy of the Agnes level. The city is protected by 41-foot-high levees.

In the Harrisburg suburbs, Central Dauphin students were kept at a high school and elementary school until authorities determined the buses could safely get the students home. Classes on Thursday were being delayed by two hours.

At least five trailer parks and campgrounds were evacuated Wednesday, Angell said, and shelters were set up in some counties for residents displaced from their homes.

The Red Cross set up six shelters in and around Harrisburg and Lancaster and another nine were being prepared or already open in and around Scranton and Wilkes-Barre in northeastern Pennsylvania.

In Easton and Allentown, in eastern Pennsylvania, the Delaware and Lehigh Rivers were expected to hit flood stage, but major flooding was not anticipated.

Amtrak suspended train service between Philadelphia and Harrisburg because of fallen trees on the tracks and damage to the overhead power lines. Late Wednesday afternoon, the company said it could not estimate how soon service would resume.

Elsewhere, the rain Tuesday and Wednesday left hundreds without power. Allentown-based energy company PPL Corp. listed roughly 500 customers without power in York County in south-central Pennsylvania, with another 300 without power in Pike County in the northeastern edge of the state.

The additional rain is on top of the downpours brought by Irene less than two weeks ago.

Near Harrisburg, at their home along Yellow Breeches Creek in Camp Hill, Karyn and Rob Brenkacs spent Wednesday morning preparing for more flooding. They and their school-age children had been been forced to spend three months in an apartment following an April flood in their house.

"We just moved home," said Karyn Brenkacs, 39, the operations manager for a financial services company. "I just unpacked last week."

The Brenkacses moved furniture and other property to the second floor of their colonial home or elevated them on the first floor in hope of keeping them dry.

"We're trying to put our washer and dryer up on cinderblocks," she said. "Everything is at least 3 feet up."

In Marietta in central Pennsylvania, residents and officials were keeping a close eye on the Susquehanna River, which was forecast to crest Friday at 59.4 feet, more than the 56 feet it reached during storms in 1996 and 2004.

Armas reported from State College, Pa.