Yes, D&G and the whole west coast can be pretty moist. I had a house near Ayr until I sold it this year. There seems to be a little dry climate zone in that area and around the southern uplands. Often I could get a day's local riding in sunshine but looking south west towards the Galloway forest it was as black as your hat and the same north to the central belt and Lomond. I have a friend who lives near Loch Lomond and he says he's barely had a dry day at work this year.
Perthshire is bad as well. I don't think I've ever ridden or driven through Pitlochry on the A9 in dry weather.
It's much better in the north east. I usually find it's a case of look at the sky on the day and pick a direction. If it's black over the Pennines, head for Northumberland, Berwickshire, the Borders and you'll likely get away with it. If it's black to the north east head the other way towards the Pennines.
The bugbear is by the beginning of October County Durham will send the gritters out.