NEW YORK - A major winter snowstorm lashed the United States east coast Sunday, and blizzard warnings are posted along the shoreline and in New York. Snow has already started falling in New York, but heavy snow whipped by strong winds later Sunday was expected to make travel very difficult or impossible through much of the region. Up to 20 inches of snow is possible. Blowing, drifting snow may cause whiteout conditions and zero visibility in places. Light snow began to fall across New York late morning, and it will get more steady and heavy throughout the day. The storm will strengthen rapidly over the next 24 hours as it moves up the eastern seaboard. City officials were encouraging people to stay off the roads beginning Sunday afternoon, because of poor visibility and hazardous conditions. Cars drivers were told to stay off the streets. Sanitation officials began to run 365 salt spreaders, and more than 1,600 snow ploughs would clean the streets once two inches of snow fell. All 4,800 sanitation workers will be out in full force, working two 12-hour shifts to take on the snowy and icy streets. Meanwhile, close to 1,000 flights across the northeast are already cancelled.