What clothing is appropriate to wear in Beijing, Shanghai, and Xian in the Springtime?

I'm traveling to Beijing, Shanghai, and Xian within ten days near the end of March. I will also be walking an average of 16 km a day. What will the temperature most likely be like? What clothes are appropriate to bring for these activities? I will also be attending a formal dinner at a couple's house in Beijing. What are appropriate formal clothes in China?