First of all a 3 month old puppy should not be outside unattended, and a pup that young should not be subjected to harsh weather without supervision. I live in Canada and while my pups are routinely outdoors in sub zero temperatures, they are under constant supervision. I suppose with multiple dogs it may be ok, but I wouldn't.
No. A young puppy needs to be protected from everything outside. And he needs that time with you to bond as well. Just don't do that to him. He will learn all kinds of problem behavior and you'l be back asking for advice on how to cure it. Why don't you want the pup inside or do you live outside as well?
Jesus, I have read through the various responses you've gotten, and IMO, they are ALL, without exception wrong! I bought my current puppy in March of 2017, which by the way, is one of the two snowyest months of the year in Colorado. My puppy had NEVER been inside a house until I brought her home. So 40s or even 30s mean absolutely nothing to a GSD puppy - unless they've always been inside and haven't been acclimated to the cold. And even then, if they have a house or kennel to snuggle up in, they're fine!
My own puppy almost couldn't be called in when temps went below zero F here, she seemed to just love it!
But keep it in mind, it's more about "drastic change in temps" than it is about current temps! If in doubt, watch or check on them frequently. I think you'll see that it takes temps much below 32 to make even a small puppy cold!
I wouldn't leave a pup that young out even in perfect weather. There is so much they need to learn about living in a human world, and they do that best by being with people.
As far as temps go, I find my dogs have a harder time with humidity than temperatures. It can be 69 F and have a dew point of 90%. A few miles walking in that and my dogs start to slow way down.
Why even have a dog if you just leave them outside. I understand some are used for various reasons, guarding sheep, goats, sled dogs even sport dogs but if your just getting one to just leave it outside no reason to have one.