What clothes should I wear to Gannan in western Sichuan in late May?

Gannan is located in the Qinghai-Tibet Plateau, and the climate is relatively wet and cold. Even in May, the temperature difference between morning and evening is still relatively large (except for Diebu and Zhouqu County No.7, which is better). In other places, coats and trousers must be worn in the morning and evening. In case of rainy weather, the temperature is generally 14 or 5 degrees. Due to strong ultraviolet rays, locals generally don't wear short sleeves.