Tiger Moth,
Back in the days when Welshpool did three week residential courses, I saw guys book three weeks in the summer and never get airborne due to crap vis or whatever. Meanwhile, having moved heaven and earth to get my PPL in the summer so I could fly over Snowdonia to Caernarfon, I got my licence and made it across the mountains in October, my first flight as a qualified pilot. And also the only time I've made it over Snowdonia ever.
And after cancelling flying the London Helicopter Routes several times, we made it on a lovely day in mid-December; only problem was barely making it home before sunset.
The weather is unpredictable in the UK, all year. I've been flying for five years; I'm beginning to know.