Hundred of thousands are without power as the storm moves across the state.
A one-two punch of rain and high wind from a monster hybrid storm that started out as a hurricane battered Pennsylvania leaving three dead.
At least three deaths were attributed to the storm. They included an elderly Lancaster County man who fell on Sunday from a tree he was trimming in advance of the approaching storm.
An 8-year-old boy died when tree limb fell on him in Franklin Township, north of Montrose. And in Berks County, a 62-year-old man died after a tree fell on top of a house in Pike Township near Boyertown.
The storm soaked Philadelphia and its suburbs Monday night, but the greatest impact was expected overnight and today, with lashing winds expected to top out at or above 50 mph and several more inches of rainfall projected for the flood-prone state.
Major interstates around Philadelphia were closed Monday evening after highway speeds had been lowered to 45 mph on interstates in the eastern part of the state. Additional road closures were likely in the day ahead, as the center of the storm was forecast to hit Harrisburg before turning north toward State College.
"We ask everybody to stay inside and stay of the roads, if possible," the governor said.
Corbett set up shop inside the Pennsylvania Emergency Management Agency headquarters outside Harrisburg, where top aides and Cabinet members were providing running updates and helping make spot decisions as events unfold. He activated 1,600 members of the National Guard, making them ready for deployment to trouble spots.
"This is going to be an event that for a period of time is going to alter the way we do things," Corbett said.
Signs of danger early on
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A sign warns drivers Monday near downtown Philadelphia ahead of Hurricane Sandy's landfall.
The severity of the storm in Pennsylvania expressed itself during the day Monday through a set of increasingly worrisome numbers, from the hundreds of people who fled their homes in the southeastern part of the state to the power outages, more than 300,000 by early evening.
The Lehigh Valley saw more than 300,000 home without power by midnight.
The greatest risk of flooding was in counties along the state's southern border, Corbett said: Chester, Lancaster, York and Adams. While officials were cautiously optimistic about the Susquehanna River, flooding in low-lying areas and for some smaller creeks and streams was considered a certainty. About a third of the state was at risk for moderate flooding, and 23 counties set up emergency operations centers.
Government offices, many courts and countless schools were shuttered on Monday and planned to remain closed at least through Tuesday. Corbett extended Tuesday's absentee ballot application deadline for a day or two for counties where the courthouses were closed Monday, Tuesday or both.
'Not going through this again'
The Red Cross set up 58 evacuation centers that could shelter 31,000 people. Hundreds of people were evacuated in the Philadelphia suburbs of Bensalem Township and Darby Borough, where officials feared overnight floods.
I'm not going through this again," said Sheila Gladden, who left her home in Philadelphia's Eastwick neighborhood. "They're telling me this is going to be worse than (1999 Hurricane) Floyd because this is some superstorm. I'm not going back until the water's receded."
Bensalem Public Safety Director Fred Harran said it was better to get residents near the Neshaminy Creek out early than deal with a dangerous situation at 2 a.m.
"It could be the worst we've ever seen," he said.
Conditions in some areas of Pennsylvania could involve winds of 75 mph and 10 inches of rain, and forecasters said the strongest winds would be in a section of the state running from the northeastern corner down to Philadelphia, and west to Harrisburg and the rest of the south-central region.
Power outages start early
The combination of rainfall and sustained gale-force winds had emergency officials particularly worried about electric lines, and the early reports seemed to confirm their fears. Some trees have not dropped their leaves, presenting a greater hazard for falling limbs. About 3,000 repairmen from Ohio, Kentucky and Chicago were poised to help the state's utilities restore service.
"People are starting to have power outages with not even the strongest of the winds here yet," said Mike Dangelo, a meteorologist with the National Weather Service in State College.
Darby Mayor Helen Thomas said her town opened its recreation center to more than 150 people that had to leave their homes. Local businesses were helping to feed evacuees.
"We're going to do what we've got to do to help our residents," she said, adding, "we won't turn away anyone."
President Barack Obama signed an emergency declaration for Pennsylvania early Monday that will allow state officials to request federal funding and other storm assistance.
In portions of western Pennsylvania, the National Weather Service issued a flash flood watch for areas that could get more than 2 inches of rain Monday and Tuesday, causing some flooding along small streams or where drainage is poor. Snow was expected later in the week.