That's Like White Snow - S1.E11

Saku's astronomy club participates in a winter stargazing camp with the girl from Takami Girl's School, who also participated in the Autumn Stargazing Conference. Saku, Edogawa and especially Hime do not dress warm enough, and while Saku and Edogawa brought more warmer clothes, Hime cannot dress in layers with the extra clothes she brought. After spending the first day freezing, Hime goes out at night to go to a local convenience store, but it is already closed by the time she gets there and a blizzard is blowing in. Hime tries to get back to the cabin, but quickly gets lost. The others notice she is gone, and also suspect Mihoshi went out to search for her. With Hime close to freezing to death, Mihoshi finds her and the two wait out the blizzard in a small snow cave. They find they were not far from the cabin and while they are scolded for what they did, everyone is relieved to have them back safely.