Soil temps may be higher, but how can you explain why the snow
settles
on cars, grass and decking. The fact the these accumulations are very
slushy even as they fall suggests to me that it is the air aloft
which
is just not cold enough - rather than the soil. Surely if the soil
was
too warm it would not settle in the first place.

It barely settled with the temp at freezing, which is why I'm pointing
the finger at soil (and concrete) temps. Cars are usually the first
place frost and snow accumulate. If the air aloft was too warm for
snow, wouldn't we expect freezing rain or ice pellets in these
conditions?

Edmund