"For instance, if I look out of the window when I get up each morning and say "sod it - I wish this bloody rain would stop" - as I invariably have over the last two years, is that folklore?"

I would say that it is not. If it happened that you said it every day regardless of the actual weather, then perhaps it would be a tradition by now. It would be one only within the confines of your household however.
I do think you are right in attaching the label folklore to the beliefs, stories and activities of a social group. I might have a quibble over "identifiable" though, since social groups are often so fluid. For example, Folk Enthusiasts and Motorbike racers are clearly separate groups, whether they are communities or not, but at different times I am a member of one or the other- but rarely both at the same time, and it is possible to affiliate or disaffiliate instantaneously.
The actual meaning of community is a tricky one. People talk about the gay community, or the immigrant community. I'd say that this is a misnomer. These are no more than social categories.
Maybe I got it from Weber, but to me 'Community' implies some communal communication across the whole group, and the growth of multiple role relationships within the group.
A family may have family folklore- mine does.
A town may have folklore- the town hall lions in Leeds, for example.
Owners groups may have folklore- the "Macs never crash" meme amongst computer users is an example.
But I would not regard the habitual or obsessive compulsive behaviour of an individual, however mild, as folklore because of the lack of social dimension.
Though, as I said, I do believe that an individual can create and maintain personal traditions.
Cheers
Dave