Summer months are best - between May and September.
Snowdon is 3,560 feet high. Temperature drops 5.4 F per 1,000 feet of elevation.
This winter has been very warm so far.
So the snow will clear early if it continues to be warmer than usual.
You'll see the current Temps before you go up clearly displayed.
The weather can change suddenly so pack for wind, rain, sun and snow !
The Mountain doesn't warm up. It depends on which way the wind blows.
From the South = warm
From the North =cold
http://www.youtube.com/watch?v=VBGmUYNRqdI
or if you're a serious Mountain Climber
http://www.youtube.com/watch?v=E4bqXTr-xbU