Coming Down like stair rods"

[hobbitess]

Does anyone know the origin of this phrase ?

[dzug]

Stair carpets used to be held in place by stair rods - long thin metal poles that were fixed onto the wood on each step with brackets either side of the carpet.

The analogy with heavy rain is obvious

[Quizmonster]

The earliest recorded use of 'stair-rods' to refer to heavy rain - rather than an actual rod to hold stair-carpet as described by Dzug above - was in an article in The Times in 1963. That may possibly have been the origin.

[hobbitess]

Thank you both

[Quizmonster]

If you can prove it, mate, The Oxford English Dictionary (TOED) will be delighted to hear from you! It certainly seems odd - if what you say is true and I have no reason to doubt you - that no-one ever wrote it down anywhere during the 'missing' two decades.
I was a child in the 40s, too, and I certainly never heard it then. Over to you and TOED!