World golf number one Lydia Ko admits it'll be a challenge for her to retain her Swinging Skirts title in San Francisco.
The 17-year-old New Zealander is about to tee off in her opening round in the defence of her title at the Lake Merced Golf Club.
Not known as a long hitter, Ko admits the cold-foggy conditions will test her especially after having a week off in the heat of Orlando.
"To come to totally different weather... I knew it would be different, but to be this cold is quite a change," she said.
"I think the biggest difference is the ball flies further, so I feel like the course if playing a little longer compared to last year."
The $2.6 million also includes world number two Inbee Park, along with Yani Tseng, Michelle Wie and Paula Creamer.