I'll assume you haven't been through an Alpine tunnel on a rainy / snowy day, only to come out at the other side to bright sunshine and just a few clouds drifting over from where you've came from! When I was in France last December, there was a freak, 'storm of the century' dumping of a metre. The Italian border was just a few miles away, although had 4000m peaks on it. Ski resorts in the next valley over received a mere dusting, and this became the case throughout the first half of the current ski season. In short, the rain shadow effect is much stronger there, you probably just have more experience of Welsh and English mountains.