The storm, a huge bluish blur on meteorologists' radar screens that stretched more than 700 miles from Indiana to Long Island, promised to be the first test of New York City's new mayor, Bill de Blasio. In his last job, as the city's public advocate, Mr. de Blasio was critical of the response under his predecessor, Michael R. Bloomberg, when a snowstorm hit in late 2010 and plows were slow to reach some neighborhoods, particularly in the boroughs outside Manhattan.

On Thursday, less than 24 hours after being sworn in as mayor, Mr. de Blasio met with the sanitation commissioner, John J. Doherty, a temporary holdover from the Bloomberg administration, and declared that the city was "ready for whatever hits us."

"We have literally all hands on deck," he said, adding that the city would face not only snow but also ice, strong winds and "a lot of different features here that we have to be ready to deal with." For starters, he urged New Yorkers to "get off the streets this evening so Sanitation has the optimal conditions to work."

"The one thing they need us to do," he said, "is get out of the way, so they can do the work."

Forecasters warned that the snow would be heaviest overnight and would continue until midday on Long Island, which they said would face the highest accumulations. Gov. Andrew M. Cuomo said the Long Island Expressway and the parkways on Long Island might have to be shut down.

"It's a nor'easter," said Tim Morrin, a meteorologist with the National Weather Service in Brookhaven, on Long Island, adding that he had no doubt about what kind of precipitation the storm would deliver: "It will be a snowstorm across the entire area."

It had swirled and blustered across the Midwest, leaving behind as much as nine inches of snow in the Chicago area since New Year's Eve and four to six inches in Ohio. But its late-day arrival in the New York metropolitan area made Thursday a day of anticipation under a gloomy, gunmetal sky.

Hardware stores were busy as people bought snow shovels and salt. Plows prepared for duty on Friday, and Mr. Morrin warned that they would not have an easy time. He said the snow would be fine and powdery, and winds of 30 to 40 miles an hour could blow it back onto roadways almost as soon as they were cleared.

Mr. de Blasio met with his deputy mayors and senior advisers on Thursday before going to the Sanitation Department's offices on Worth Street in Manhattan for a briefing. Officials said First Deputy Mayor Anthony Shorris had been in touch with state officials and regional transportation agencies. The Sanitation Department issued a snow alert at 1 a.m. Thursday, and alternate-side parking was suspended for the day.

Officials said that 450 salt spreaders had been out since early Thursday morning and 1,700 sanitation trucks had been outfitted with plows.

The Metropolitan Transportation Authority said it was planning to salt train platforms and send out "de-icers" and "snow and ice-busting equipment" to keep outdoor subway tracks, switches and third rails clear as the snow fell.

While the underground system should otherwise be unaffected, the authority said that outdoor stretches of the Rockaway, Sea Beach, Brighton and Dyre Avenue lines were particularly vulnerable to snow. Some subway trains were to be moved underground to prevent them from being stuck in chilly outdoor storage yards, even though parking them inside could limit express service on some lines.

Platforms on Metro-North Railroad and Long Island Rail Road were also being salted, the transit agency said, and the railroads were turning on devices to heat their switches, lubricate them and treat them with "antifreeze agents."

With airline cancellations or delays expected, the Port Authority of New York and New Jersey urged travelers to check on the status of their flights in advance.

The storm will be the first in which the transit agencies are interacting with the de Blasio administration, but officials' conversations will probably feel familiar. Adam Lisberg, the chief spokesman for the transportation authority, said the primary points of contact in city government, particularly at the Office of Emergency Management, were essentially unchanged. Mr. de Blasio has asked top officials at the sanitation and emergency management agencies to stay on the job temporarily.