Pittsburgh Mayor Luke Ravenstahl declared a state of emergency on Wednesday in anticipation of flooding expected to occur this weekend.

"We are going to experience flooding, there's no doubt," Mr. Ravenstahl said before briefing City Council members on the situation. He said the severity could be comparable to the January 1996 flood, considered among the worst in the city's history.

The mayor said the emergency declaration was intended to make it easier for the city "to have every resource we need to fight the flood." It allows the city to bypass formal competitive bidding procedures to obtain equipment and supplies.

The declaration has no immediate impact on citizens, but it was also intended to raise awareness of the possible danger and motivate residents to prepare.

"People I talk to casually are surprised to hear a flood is coming," he said. "They don't believe it's going to happen."

Mr. Ravenstahl said the declaration would not affect plans for the annual St. Patrick's Day Parade on Saturday. He noted that the parade went on despite a blizzard in 1993.

The National Weather Service has issued a flood watch for all of southwestern Pennsylvania, much of eastern Ohio and northern West Virginia from tonight through Sunday night.

A watch means there is a "potential for flooding based on current forecasts of snow melt and rainfall." A warning, which had not been issued as of Wednesday night, would mean flooding has occurred or is imminent.

In his presentation to council, Mr. Ravenstahl said the weather service was expecting rivers to crest at 27 to 32 feet over the weekend. Flood stage is 25 feet. A crest at 32 feet would swamp Point State Park, the 10th Street Bypass and the Parkway East "bathtub" as well as low-lying residential areas along the rivers. The crest in January 1996 was 34.6 feet.

But the mayor and a weather service hydrologist both said there is much uncertainty about what will happen this weekend.

"We're trying to stay away from specifics until we have more certainty," said hydrologist Bill Drzal. "You can't talk in certainties right now."

Computer models for rainfall this weekend are changing by the day, he said. The other variable is how fast the deep snow in the Laurel Highlands and at other areas of high elevation will melt.

In Garrett County, Md., unmelted snow holds moisture that is the equivalent of 10 inches or more of rain. That area drains into the Youghiogheny River, which flows into the Monongahela.

"This is one of the largest snowpacks in history in these mountains this late in the year," said Michael Huss, city public safety chief. "This is a very unusual situation."

City officials urged residents to prepare for weekend flooding by preparing emergency kits with 72 hours of supplies and monitoring weather forecasts. City employees will go door-to-door to distribute information about evacuations in flood-prone neighborhoods, Mr. Ravenstahl said.

The city also is prepared to open shelters for any residents forced to evacuate, he said.

A city website, www.publicsafety.pittsburghpa.org, has tips on preparing for flooding, maps showing which city neighborhoods are affected by various flood levels and a place to sign up for emergency alerts.

The Red Cross said Wednesday that 17 evacuation teams were on alert and ready to open shelters in southwestern Pennsylvania.

Should the need arise, the Red Cross will join with municipalities and community groups to open additional shelters, said CEO Patricia Waldinger.

"Our volunteers are trained and prepared to respond to disasters, so should our region be affected by flooding, the Red Cross is ready to help," she said.

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