In reply to jules699:
I did the Welsh 15 peaks over New Year and was bivvying on Y Garn.
It was minus 15 from what I remember. Lovely clear night and you could see fireworks in every direction.
There were two tents from memory on the sides, but I slept on the summit in a alpkit hunka and mountain hardware lamina 0 on a M E five season mat.
Very memorable and a good challenge (I was in good shape and well prepared). Stocked up in Nant Peris and dropped off rucksack for a day sack, after getting up and making breakfast, seeing sunrise from Elidir Fawr.
Ran down from Snowdon to car in Nant Peris and got back for a family New Year's Day dinner