Raining "cats and dogs" is a euphemism for a heavy downpour. Each drop of rain is euphemistically the weight of a cat. When that occurs, the earth is ten times more cleansed than occurs during a light drizzle. When the earth is spiritually cleansed, it will be as though it were raining cats and dogs every day for as long as it takes to complete the cleansing. It will rain cats and dogs for an entire year, if necessary.
In the spirit realm, it rains cats and dogs when the ether can no longer carry the load of sin, and the heavens open to release whatever it is carrying, whether snow, rain, or the consequences of sin and transgression. In the context of sins of omission, a heavy downpour might constitute an electricity blackout. Where the transgression is the failure to tithe, a heavy downpour might constitute famine. Where the sin of omission is a lack of compassion, a heavy downpour might constitute living in constant fear.
The Lord God Almighty El Shaddai