Glacier - Waterton National Park Weather Glacier National Park, like many mountain parks in the west, is a slave to the seasons. Long cold winters restrict the bulk of visitor use to the months of June, July, August and September even though the park is open year-round. Most park services and facilities are available from late May through September. Summer rainfall averages around two to three inches per month. F. Up slope, in areas above treeline, it is frequently 10 to 15 degrees cooler.
Strong winds predominate on the east side of the park.
Overnight lows throughout the park can drop to near 20 degrees F, and snow can fall anytime. In August of 1992, a foot of snow fell on the northeastern corner of Glacier. Prepare for a variety of weather conditions and pack accordingly. You may start the day in a T-shirt and shorts and need a parka by evening. Dress in layers.