A weekend winter weather advisory was issued Friday for most of Long Island, with 2 to 4 inches of snow expected to start falling this morning.

The National Weather Service advisory for Nassau and western Suffolk goes from 8 a.m. Saturday to 6 a.m. Sunday. It forecasts higher accumulations away from the Island's South Shore Saturday.

Chance of precipitation is 90 percent, meteorologists said.

The snow will mix with rain or change to rain briefly in the afternoon before tapering off Saturday night, the Upton-based service said. The likelihood of rain is higher on the South Shore, the advisory said.

The moderate snowfall makes conditions dangerous, the service warned. Visibility could fall to a quarter-mile or a half-mile at times, the advisory said.

Saturday's daytime highs will be in the 30s and nighttime lows in the high 20s.

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"We're still expecting some snow on Long Island, but the question is how much rain is going to get mixed in," said meteorologist Lauren Nash of the Upton-based service.

Sunday will be partly sunny and breezy, with daytime highs in the mid-30s and temperatures in the low 20s at night, the service said.