It was the first career win in the giant slalom for Weirather, who edged second-place Lara Gut of Switzerland by 0.73 seconds and nudged her out of the overall lead.
"It was a great Christmas gift," said Weirather. "To win a giant slalom means a lot. The GS has always been the discipline in which I wanted to do well."
Weirather turned in a combined two-run time of 2 minutes, 24.10 seconds on the course, which is seldom used for giant slaloms.
Sweden continued its recent streak of World Cup podiums with a third-place finish by Maria Pietilae-Holmner. It was the first time Pietilae-Holmner had finished in the money in the giant slalom. Her time was 2:25.05.
Mikaela Schffrin took eighth place and was the top U.S. finisher. Maria Hoefl-Riesch finished 11th and was in third place in the overall standings at the end of the day.