I'm planning to do some backyard smithing this winter. What changes in metal properties from cold temperatures have you experienced. Anything a newbie may not be aware of? Are there safety issues that need addressed besides, of course, dressing for the weather. Thank you.

The difference between 70F to 2000F and 0F to 2000F isn't gonna make much difference to the steel. Your anvil will suck the heat out of your piece faster and you will want a glove on your holding hand as cold steel gets uncomfortable pretty quick.

Frosty may be able to answer this question with some authority,

I would suggest prewarming the anvil, and cold metal can freeze to naked skin, so care in handling, I am sure others will enlarge upon these basics

Have fun