In reply to ijsbeer:
I would think about heading to the far north west of Scotland, Torridon, Gairloch, Lochinver. Bad weather seems to hit Skye and the Fort William area, but it is often surprisingly nice north of that. Also, the scenery is stunning and there is some great hillwalking.
The weather is changeable in the UK as a whole, so as others have said, you could actually put off the decision until you get here - you could go almost anywhere in Scotland or northern England quite easily so you can wait until you have more up to date forecasts.
Having said that, the weather is changeable all over the UK - if you take the risk and go out anyway, and have flexible plans, it is often surprising how much you can do, and Scotland can be at it's most dramatic in mixed weather.
Have fun, whatever you end up doing.
Post edited at 16:23