although there are several theories about the origin of this phrase, the following are the most common.
One theory is that long ago in England, the roofs on houses were made of hay, and the cats and dogs would sleep on the roof. When it rained, the roof got slippery and the cats and dogs would slide off. Hence, it was raining cats and dogs Another explanation is that heavy rains would wash dead animals down the streets. However, the most popular one comes from Northern European myths in which cats were a symbol for rain and dogs for wind Thus, a heavy rain storm with strong winds was described its cats and dogs out there