Although today's weather forecast changed several times Tuesday, PennDOT's response plan didn't.
"Mother nature changes," spokesman Jim Struzzi said. "Better to be safe than sorry."
The storm was expected to hit southwestern Pennsylvania later and leave behind less snow -- 1 to 3 inches overnight and another 1 to 2 during rush hour -- than was forecast earlier that day, according to the National Weather Service.
A 70-plus fleet of snow-removal trucks waited for the snow to arrive Tuesday night. Responsible for interstates and main arteries such as Routes 8, 22 and 28, PennDOT was in "full force" overnight clearing roads before the morning rush, Mr. Struzzi said.
PennDOT will concentrate on those thoroughfares, then attend to secondary roads.
In the calm before the storm, PennDOT crews in Allegheny County checked equipment for mechanical problems, ensured materials were stocked and mounted plows on its trucks.
Between 1 to 3 inches of snow was expected to fall in southwestern Pennsylvania overnight, weather service meteorologist Brad Rehak said, with an additional 1 to 2 inches settling in for this morning's commute.
"We should still have snow during rush hour," meteorologist Bill Modzelewski said.
The heaviest snow will be tapering off as the earliest commuters hit the road, he said.
Slick spots on the roads could create hazards, and drivers are urged to check the forecast in the morning and adjust travel plans accordingly, authorities said.
Tuesday's fluctuating forecast was caused by the storm's shape -- a narrow and heavy band, Mr. Modzelewski said. Because the storm was narrow, it was more difficult to predict where the heaviest snow would hit, he said.
This storm drew "a sharp line" through the region, Mr. Rehak said, with areas north of that line expecting significantly less snow than southern areas.
"That line will be drawn very close to Allegheny County," he said Tuesday night.
A winter weather warning is in effect for Pittsburgh and areas south through 5 p.m. today.
Parts of Washington, Greene and Westmoreland counties could see between 4 to 8 inches of snow, and higher elevations in Fayette and Westmoreland counties could see up to 9 or 10 inches.
A winter weather advisory in Beaver, Butler, Armstrong and Indiana counties could bring between 3 and 5 inches of snow through 4 p.m. today.
On Monday, Mr. Rehak called this "probably the last big snow" of the winter.
By Tuesday night, northern Illinois and Indiana had been hit hardest by this storm, accumulating about 5 to 8 inches of snow, with 6 inches in Chicago, he said.