The going to the sun road is already closed. Not sure if the area around McDonald lake closes in December. I was up there last week and all the shops were closed. They didn't have any snow then, but I bet they do now.
Was there this summer after growing up near there. Depending on whether the park usually closes in October and opens in early June or July right now Montana is experiencing very cold and snowy and windy weather. I just Googled it !!!
Based on what their website says and what I heard from a park ranger, the park itself is open all year round but the buildings may not be open at all or as often. Here is a link to the page I looked at to find their hours and seasons of operation. https://www.nps.gov/glac/planyourvisit/basicinfo.htm
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