It will be very cold then and snow may also happen. Please wear your warmest winter clothes, sweater, down jacket, woolen trousers and jeans. However, most days will be plenty of sunshine during daytime.

As for travel, five days will be enough for you to explore this city entirely. The must ones should be the famous Terra-cotta Warriors and Horses, Xian City Wall, Bell and Drum Tower, Big Wild Goose Pagoda, Shaanxi History Museum.... Of course, don't miss the local food. Suggested that you refer to the recommended Xian Tour Packages(https://www.travelchinaguide.com/package/xian.htm)