In reply to mountaingoat42:
I walked this last weekend, and ran in early Jan last year.
To give you and idea on what the conditions can be like, here are my photos from last weekend:
https://www.facebook.com/media/set/?set=a.10154072235881021.1073742040.6196...
And a video from early Jan last year:
As the posts above have said, conditions vary dramatically on a daily basis.
Prior to our visits we monitor daily two key websites to judge conditions:
1) Summit weather forecasts:
http://www.mountain-forecast.com/peaks/Snowdon/forecasts/1085
This gives 6 day and 9 day forecasts on summit conditions. This is really key as summit conditions can vary hugely from those at the foot of the mountain. Understanding and preparing for conditions at the summit is critical.
2) Ground condition reports:
http://www.eryri-npa.gov.uk/visiting/walking/ground-conditions?name
Some very kind and helpful Snowdon rangers (plus helpers) walk up Snowdon every few days and post details and photos of the conditions under foot. This is just as important as the forecasts. As it might not be forecast to snow, but knowing what is already on the ground already is equally important.
I echo the comments about the need to be cautious and be prepared to carry crampons/ice axes.
Last year I only had microspikes (
https://www.ukclimbing.com/gear/review.php?id=3268) and vowed I would not do it again without full crampons/ice axe. This year we had the gear packed in the car ready, but based on the forecast and ground conditions reports decided to stick with just microspikes in the end. And it was quite sufficient.
For maximum enjoyment, my recommendation would be to do it in summer first, and enjoy the mountain whilst learning the route. Then return in winter and deliberately plan a trip when there is good snow. And having bought the right kit (ice axe/crampons) and learnt how to self arrest. You'll see the mountain in a completely different light, but without taking undue risks.
Paul.