I have just read your thoughts on the phrase 'Raining Stair-rods'. I seem to remember that this phras was coined in the early days of photography when the aperture shutter speeds were very slow.
When a photographer took a photograph in the rain, the rain was recorded on the film plate as a long thin bar, similar in appearance to a stair rod.
The ruined photograph was then said to be ruined "Because it was raining stair rods".