I had a chance to practice some more local vernacular (Reet' Parkey). On Friday, having taken a day off work, under a bright blue sky and in spite of forecast for showers, I went for a row.
Just after I'd started on the return trip and about 3 miles from home, the sky grew dark, the wind picked up and the heavens opened - "coming down in stair-rods". For those not familiar, wooden or metal rods were used to secure carpet to stairs year ago, probably dating back to Victorian times, but I can just about remember them from when I was very young.
Needless to say it's a good metaphor for heavy rain. In fact on the day, it was so cold there were hail stones, but I don't remember any slang for those.
By the time I got back to Swanwick Hard the rain had stopped, everything was very still and the sun was starting to come out again.