I think I was lucky last year....I hardly had any cancellations due to weather...and the club I was at could reschedule 'after-work' flights at very short notice.
Just keep keen, and battle on...it won't happen every time.
Also, if the vis isn't great ask if you can have a go at going around the circuit, where long range vis isn't necessary.
Also if you've had 4 lessons cancelled..thats 4 lots of £80 saved, so you during the next spell of decent weather you can try cramming a few more lessons in.