Permafrost

Not really. That's what you get in the Russian tundra - or used to - not sure now, what with global warming and all.
But I was reminded of the patterns frost can sometimes make on glass, under the right conditions (and this is etched, so it's permanent, hence...).
And today was bloody cold, as is only proper at this time of year.

(Thanks for the lift Norma - that bag of stuff for the post weighed 12 kilos!)