frost free period meaning in English

解冻期
无霜期

Zhoushan has a northern subtropical monsoon marine climate with clear four seasons ; leading wind directions are southeast wind in summer , northwest wind in winter . with an annual average wind speed of 3 . 3m s ; and an average temperature of 15 . 6 - 16 . 6 , and the frost free period reaches 251 - 303 days perannum , annual average sunshine time 1941 - 2257 hours , and the annual preeipitation is 927 - 1620 mm
舟山属北亚热带南缘季风海洋型气候，四季分明主导风向，夏季为东南风，冬季为西北风，年平均风速3 . 3米秒年平均气温15 . 6 . - 16 . 6 ，冬季最低温为- 1 ，夏季最高温度为37无霜期251 - 303天，年日照时数1941 - 2257小时年降雨