A pre-Christmas snowstorm paralyzed parts of northern Greece, with hundreds of motorists stranded on a blocked highway in Macedonia early Friday. The storm began late Thursday, Ekathimerini reported. The Egnatia Odos highway came to a standstill after a tractor-trailer skidded and overturned. About 500 people were stuck on the highway, officials said. A school became a temporary shelter. An official with the company managing the road said it was cleared by late morning. High winds left about 50 villages in northern Greece without electrical power. Even in the Athens region, drivers were warned to use chains if they ventured into mountainous areas. Forecasters said temperatures were expected to be higher late Friday and Saturday, with overnight lows around 30 F in the north.