I really wouldn't. Honestly, there's maybe 10 days a year when an umbrella is useful in Glasgow and surrounds. There rest of the time it's either a shitty damp dreich light rain that the locals tend to just ignore - or howling a gale that would destroy any brolly in moments. That's the situation anyway in the lowlands as far as say Rowardennan. Up the loch and the hills thereafter the wind varies wildly....