风雨交加，形容雨势较大。
Also, rain buckets. Rain very heavily, as in It was raining cats and dogs so I couldn't walk to the store, or It's been raining buckets all day. The precise allusion in the first term, which dates from the mid-1600s, has been lost, but it probably refers to gutters overflowing with debris that included sewage, garbage, and dead animals. Richard Brome used a version of this idiom in his play The City Wit (c. 1652), where a character pretending a knowledge of Latin translates wholly by ear, “Regna bitque/and it shall rain,Dogmata Polla Sophon/dogs and polecats and so forth.” The variant presumably alludes to rain heavy enough to fill pails.
（摘自：
http://www.dictionary.com/browse/rain--cats--and--dogs）
罗森指出，该短语有更早的一种变体，“Rain Dogs and Pole cats”，（“下狗和鸡貂”），来自理查德·伯罗米的《1652年城市妙语》。关于这一起源的意见包括：
·古体法语Catdoupe意为瀑布或大瀑布。
·雷电大作与猫狗打架的声音相似。
·北方神话中，猫对天气会产生影响，此外，暴风雨之神欧丁（Odin）是由狗和狼侍俸的。
（摘自：
http://baike.baidu.com/view/1699706.htm）