The tri-state region is bracing for a blizzard that is expected to hit Monday afternoon and could measure up as one of the worst snowstorm in New York City history.

With a possibility of 30 inches of snow and wind gusts of 65 miles an hour, New York City Mayor Bill de Blasio came out Sunday with members of his emergency response team to urge residents to use extreme caution over the next two days.

"My message to all New Yorkers is, prepare for something worse than we have seen before," said Mr. de Blasio. "Don't underestimate this storm."

Forecasters have issued a blizzard warning for New York City, northern New Jersey, Long Island and most of southern Connecticut.

The storm moved through the mid-Atlantic Sunday, was expected to get progressively worse as it comes east and would "max out" as it hits the New York area, said John Cristantello, a meteorologist with the National Weather Service.

Lighter snow is expected to begin midmorning Monday and turn heavy around the evening commute into Tuesday morning, with sustained winds from 30 to 40 miles an hour, according to the weather service. Accumulation will be at least 20 inches across the region and temperatures will be in the 20s.

Whiteout conditions are possible and many roads will be unpassable, according the weather service.

Schools will be open Monday, but there will be no after-school activities. Mr. de Blasio said it is likely that school will be closed Tuesday; an announcement on school closures is expected Monday.

City officials also urged workers to either telecommute or to adjust their hours by arriving early on Monday and leaving before rush hour. Drivers should stay off the roads Monday night and all day Tuesday, said Mr. de Blasio.

Residents also should stay out of city parks until after the park paths are assessed--at least until Wednesday morning, he said. With the high winds, power outages are expected, according to city officials.

Alternate side parking has been suspended for Monday and Tuesday as have all garbage and recycling services.

The city's Department of Sanitation and Department of Transportation workers have spent days preparing for the storm. Some 1,000 potholes have been filled in anticipation of the blizzard and workers have been pulling long shifts to outfit trucks with snowplow equipment.

Ahead of the snowfall, city officials said, 500 salt spreaders will be deployed. When 2 inches have accumulated, 1,500 snowplows will be clearing the city's 6,000 miles of road.

Gov. Andrew Cuomo also urged New Yorkers to plan for closed roads and delayed or canceled public transportation and flights, and even suggested that they stay home from work if possible. State agencies have directed equipment and other resources to the areas expected to be hit hardest. The Metropolitan Transportation Authority will begin storing trains underground on Monday night, according to a statement from Mr. Cuomo.

The approaching blizzard could measure up or surpass a 1947 storm that dumped 26.4 inches of snow or a February 2006 storm that dumped 26.9 inches of snow.

"When this storm gets into the magnitude that they are projecting, there are going to be a lot of breaks in city service," said Joseph Esposito, commissioner of the city's Office of Emergency Management.

Write to Melanie Grayce West at melanie.west@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires