Ahhhhhh!!! I HOPE that's an old picture, and that you guys DON'T still have snow!!! I have never raised chicks (well...never brooded chicks). But if mama has been doing a good job as mama, she should offer protection if the chick gets too cold. I'd try it for an hour or so, and observe whether mama is tucking the chick under if he/she gets cold. If she is, then I'd certainly offer the option daily, at least during the main part of the day. We're pretty much hanging around 50 here during the day, so I'm hoping you guys are in the upper 30s or lower 40s by now. Ahhh...but now I'm rethinking, because the baby is only a week old (almost). On 2nd thought, I'd wait another week and try it. Sorry, I was no help...lol. Hopefully someone with broody experience will give you a better answer.
If you don't get one in an hour or so, try reposting with something like "Is ___ degrees too cold for new chick with mama?" or something like that...