A letter today in one of the leading national newspapers in the UK, the Daily Telegraph,  suggests that the sentiments behind the lyrics to 'White Christmas', having regard to the fact it was written in sunny California in wartime, were not meant to refer to snow at all but to purity, i.e. 'I'm dreaming of a pure Christmas' - or peaceful Christmas.

Interesting thought, but the letter writer obviously does not know about the dropped verse, rarely sung (though it does sometimes crop up)

The sun is shining, the grass is green,
The orange and palm trees sway.
There's never been such a day
in Beverly Hills, L.A.
But it's December the twenty-fourth,—
And I am longing to be up North

then of course the words with which we are all familiar

The introductory verse of many songs seems to be dropped more often than not, and to my mind at least this is a pity. They frequently help set the scene and go some way to establish a mood.