At least one inch of snow, the first measurable amount of the season, fell in the Washington area yesterday, with National Weather Service forecasters predicting an accumulation of as much as three inches before midday today.

The weather service issued a travelers advisory for the Washington area and predicted that snow during the night would bring increasingly hazardous conditions, with falling snow and below-freezing temperatures causing slightly reduced visibility and slippery roads.

The U.S. Park Police closed side roads leading to Rock Creek Parkway late last night and said the parkway itself may be closed early this morning. Crews were sanding area streets early this morning.

Temperatures were near freezing all day yesterday, as the storm system with the snow moved slowly toward the city from the west. The weather service predicted cold temperatures today, with the thermometer expected to register in the low to mid 20s early this morning and with highs reaching only the mid to upper 30s later today.

At National Airport, the weather service's official measuring station, meteorologists first reported light snow at 6 p.m. yesterday. The last measurable snow at the airport was recorded March 14 when one inch fell.

The storm front bringing the snow to Washington was the leading edge of a low-pressure system that covered much of Indiana and Ohio yesterday and was expected to sweep southeastward to lie off the Atlantic coast from New Jersey to Virginia by tonight.

Snow accumulated over West Virginia yesterday and began to fall on the mountains and valleys of western Virginia and Maryland yesterday afternoon. Winter storm warnings had been issued there, with as much as six inches of snow expected in some areas.