It rained heavily today - no wind, rain came straight down. And I was wearing a VERY light VERY thin microfibre jacket

Yes, my jacket is middleweight, not a heavy winter coat.

Like I said, I wear it in San Francisco, which isn't the arctic, but like Edinburgh gets the type of sea-blown cold that makes the thermometer quite deceptive (50 degrees in the summer here feels like 20 degrees in the winter back east).

It sounds like cold rainy days: my leather jacket and an umbrella; not so cold rainy days: a good single-layer rain coat.

But I might try Bob's suggestion, if I can make sure I can fit my flask through one of the bag's air holes.

Thanks again for the advice.

Well- when we were there and it was 45 it felt like 45 - I had on a tee shirt, a thin cotton turtleneck, a cotton sweater and an unlined raincoat - and that was enough.

If it were 20 here and you were dressed like that you would freeze - for 20 you need a heavy winter coat and sweater and shirt and hat and gloves and scarf and lined boots etc.

So - no the 50 isn;t like 20 - it;s like 50 and damp - chilly but not really cold.