Winter transition

For 3 days we have been shrouded in freezing fog.  The daytime temperature hovers around minus 1, at night it falls a few degrees.  Any moisture in the trees has been caught and frozen, but interestingly the frost doesn't settle on the ground.
We have been trying to fathom what heralds the onset of winter.  This year we have missed the snowfalls so far.  But suddenly a week ago we had a sudden transition from mild autumn to dark winter.  Iron hard ground and looking out onto this is a pretty definite indicator.