Dogs can safely be outside for at least awhile to play and get fresh air in any cold weather temperature.
However if the temperature is 35 F or below then the dog should not be left outside longer than an hour or 2 before bringing the dog back inside.
I had a dog that loved to sit outside for a few hours in the snow and would also love to go play in the snow in the yard for a few hours.
Then he would decide it was time to come back inside to warm up.
But if the temperature outside is lower than 35 F you should never leave the dog outside especially overnight to prevent the dog from freezing to death.
Even humans just like dogs can go outside even for a few minutes when the temperature is below freezing and still be safe as long as you're bundled up properly.