With snow crews battling more than 20 inches of snow, and more snowfall expected Tuesday and Wednesday, the city may not fully recover for days.

Mayor Luke Ravenstahl, in a news conference Sunday afternoon, called the next 24 hours "very important."

"We are doing everything in our power to help," he said.

The large accumulation Friday and Saturday posed a significant challenge, so much so that the mayor and Allegheny County Executive Dan Onorato both said, more than 24 hours after the snow stopped falling, that many roads remained "treacherous" and that citizens should refrain from driving unless necessary.

In addition to National Guard assistance dispatched Sunday, the city has also contracted with outside agencies to assist in clearing the roadways. The county has offered resources as well, Mr. Onorato said, though it continues the process of digging itself out from the storm.

Pittsburgh Public Schools and surrounding districts announced closures today, and the city asked nonessential employees to stay home.

The University of Pittsburgh is closed today, as are all Community College of Allegheny County and area Penn State University campuses

Area businesses will have to make their own decisions about closures, Mr. Ravenstahl said, but should be aware that parking lots may not be plowed and the commute may be difficult.

The mayor said the Department of Public Works is doing everything it can to clear the roads.

Public Works Director Rob Kaczorowski said all of the primary streets had been plowed and treated, along with 25 percent of the secondary streets and 10 percent of the tertiary roads, such as alleys. But that doesn't mean drivers will be able to see the roadway -- many of the roads that have been plowed and treated are still covered in packed snow.

With nearly three decades of snow removal experience, Mr. Kaczorowski said this is the worst snow he has had to battle.

"This is the worst," he said after 36 hours on duty. "This is worse than '93."

This weekend's snowfall of 21.1 inches was, according to the National Weather Service, the fourth highest accumulation in Pittsburgh since 1876, when the agency began keeping records. The third biggest snowfall, with 25.3 inches, was March 12-14, 1993.

Mr. Kaczorowski remembers working that snowstorm. The wet, heavy snow Pittsburgh received this weekend, compared to the light, powdery snow of 1993, makes removal "10 times worse," he said.

Fallen power lines and tree limbs, cars stuck in the roadways, people shoveling snow into the road and stranded plows have all complicated the work being done by the city's 63 trucks and tractors.

One truck working in Troy Hill on the North Side overheated and caught on fire. The driver was fine, but the vehicle is out of commission, Mr. Kaczorowski said.

Plow work has been complicated by people shoveling snow out of their driveways and sidewalks and into the roads, Mr. Kaczorowski said.

Mr. Ravenstahl said he was halting citations of residents who have not cleared their sidewalks. Garbage and recycling collection has also been suspended indefinitely in the city, he said.

Six warming centers were opened for people without heat in their homes. The city's 311 non-emergency help line remains active, though residents are asked not to use the line to make calls regarding snow removal.

Looking for more from the Post-Gazette? Join PG+, our members-only web site. You'll get exclusive sports content, opinion, financial information, discounts from retailers and restaurants, and more. Our introduction to PG+ gives you all the details.