The warm water over the Gulf Stream gives up a lot of water vapour. Winds coming from that direction pass over the mountains of the West of Scotland, the Lake District or Wales. When they do this, they lose their water content as they go. Winds coming from other directions tend to cause much less rain. The South East of England is a surprisingly dry place.
Rainfall is continuously available through the year, but some times are obviously worse than others.
Choosing When to Visit the UK Rock Climbing As you can see from the graph above, if you want to visit Scotland, April Through to June are the months to do it. Unfortunately, of course, most of the rest of Europe gets holidays in July. Many cliffs dry fast however, and it is traditional to climb many climbs in the rain. Further South it's okay to come later, but still September is a truly rainy month. Ice Climbing Choosing when to go ice climbing is an art mainly involving the use of a crystal ball, and many many druidic incantations.