Yiwu has a weather similar to London, Paris, Koeln, Maastricht, Geneva, and New York. Very much like Las Vegas and Tokyo. Warm spring, hot summer, cool autumn, and cold winter.
Spring: Mar.-Apr. Temperature: 10C/50H-25C/77H. If you go to Yiwu in this time, sweaters, suits and shirts would be enough.
Summer: Jun.-Aug. Temperature: 25C/77H-35C/95H. It rains a lot in June, day in and day out. Shorts, thin shirts, skirts would be ideal. Sun glasses, sun-creams would be a plus.
Autumn: Sep.-Nov. Temperature: 10C/50H-25C/77H. Any clothes you wear with this temperature.
Winter: Dec.-Feb. Temperature: 0C/32H-10C/50H. Winter clothes like thick coat, warm socks, gloves anything that can keep you from cold.