In reply to eschaton:
Absolutely yes. Scotland, like the rest of the UK, is often governed by Atlantic weather fronts, i.e. warmish Westerly winds bringing in moisture off the atlantic. But given a lot of the better Scottish climbing, and indeed the A82 is on the west AND close to mountains, it suffers even worse from that (although some further westerly peninsulas and hebrides can escape the rain as it blows over to dump on the hills). The general motto is stay glued to Metoffice (or site of your choice), be prepared to change your plans last minute, always go North and West if the weather allows (it often doesn't), otherwise go East when it's bad in the west. And be prepared to drive a lot.