很冷。
Hěn lěng
Very cold.
Simple
今天很冷，多穿点衣服。
Jīn tiān hěn lěng, duō chuān diǎn yī fú
Today very cold, wear more clothes.
多穿点 = wear a bit more, common advice
冻死了，寒风刺骨，出门简直是受罪！
Dòng sǐ le, hán fēng cì gǔ, chū mén jiǎn zhí shì shòu zuì!
Frozen to death, cold wind pierces bones, going out is simply suffering!
寒风刺骨 = bone-piercing cold wind, classic idiom; 受罪 = to suffer/endure punishment
More Chinese (Mandarin) Weather Phrases