In reply to Bulls Crack: For you there might be a season but for others there isn't, and theres plenty of people who will only touch grit (yep I know grit isn't the only rock type) once the frost has arrived.
Jon has about one week in the spring and one week in the autumn when the conditions are perfect and at all other times moans that it's too hot, midgey and greasy or too cold, windy and green. All of his comments are just a ruse to keep the crags quieter for himself.
op: Jons advice is good though, get out there, do loads of bouldering for the winter and only get the rope out on nice bluesky days when theres no wind. Your belayer will appreciate it.