We're talking about eating beautiful white snow. Pristine sparkling snow. Fresh snow. Packed snow. Snowballs. Cristal clear icicles.
A little bit of snow or ice isn't going to hurt anyone. If your dog enjoys an occasional snow snack, let him have at it. However, if your dog fails to imbibe winter water vapor with moderation, you may need to intervene.
You see, some dogs eat snow then throw up. Sadly, they don't seem to connect the two actions- and if they do, they don't conclude that anything undesirable has occurred. Cause and effect? Bah! This is nice cold fluffy snow, I'll just dig in! Oops! I hurled my breakfast. Hmm. Maybe I'll go ahead and eat this warm puke! Look how elegantly it is presented on this cool bed of snow!
And we yuckily come full circle.
For some reason certain dogs find consuming snow and ice irresistible. Why? Who knows? It's a bit like the Why Do Some Dogs Eat Poop debate. We will never know for sure why. Meanwhile, the more important focus ought to be on how to stop this behavior rather than playing psychoanalyst with your best friend.
One method of discouraging snow eating is to utilize the villainous snow. When the dog shoves his nose into the snow, throw a snowball at him before he has a chance to bite off a mouth full of snow. (It's the same principle that worked when he was a puppy: startle him before he takes a bite of the dining room table leg.) The snowball method only works if you have a fast and accurate throwing arm.
Another method is the always popular, shouting NO! at the dog just before he digs in for a mouth full of snow. This only works if you have already taught your dog what NO! means.
If the situation gets out of hand and you can't let the dog outside without him eating snow then vomiting, you may have to put him on a leash to do his business. That way he is focused on the task. (You'll be giving him the go potty command as you shiver in your pajamas and boots.) And if he should lap up some snow, you can use the leash to redirect him.
Keep your cool. Keep your snow cool.
Keep your socks dry.