If you want to improve the chances of snow at your British home town during the Christmas season I have a simple solution.
Volunteer to drive people down to the Whitechapel Mission in London to cook breakfast for people who are homeless.
I think that since moving to Raunds it has now worked 3 out of 4 Christmases (we didn't book early enough to get a place one year).
Anyway I'll be leaving at 4am in the morning taking a car load of clothes, good and toiletries (and 4 volunteers squashed in) and there is still snow on the roads in Raunds.
Actually, it would probably be better for people who are homeless if I stopped volunteering at Christmas as being homeless when it snows is terrible. Fortunately the Whitechapel Mission have a policy of opening up the Church for people to sleep in when the temperature drops below freezing. A lot of extra work for the staff but infinitely better than even more of their friends dying on the streets (even though I only get to go a few times a year there are people I have known where that has happened).