Glacier is a big park, so it can be rainy in the east and blue skies in the west. The best time for hiking is late June through September, when the days are longer and it’s warm enough for camping. Temperatures can range from the 50s to the low 80s. The backcountry trails are frequently snowbound until mid-summer; the main road through the park—the entire 50-mile stretch of the Going-to-the-Sun Road—is only open from mid-June to mid-September. If you’re planning to visit the park in July or August, book rooms early as this is prime tourist season. Even though it’s summer, don’t think you won’t see snow. It comes at all times in the park, especially in the higher elevations.
April through mid-June and after Labor Day are the park’s shoulder seasons. The spring is a good time to see baby elk, moose, and mountain goats—and the bear are generally out in force, fattening up for the next winter. September and October are when the elk and moose are in rut, so sightings are plentiful as the males of the species swagger around impressing potential mates. Late May (depending on snowmelt) is prime time for spectacular displays of wildflowers and cascading waterfalls. While the backcountry lodges close in September, it’s a beautiful time to visit the park, with colorful fall foliage, fewer crowds, and milder temperatures (read: no bugs).
November through March is the coldest time in the park, with snow on the ground from October through April. These months are bad for hiking, but ideal for snowshoeing and cross country skiing. The good news is that while you can’t drive through the park in the winter, the roads are open to foot traffic. From the west side, you can drive to Lake McDonald Lodge, and then continue on the Sun Road on skis. Daytime temperatures are generally in the low to high 30s, with nighttime temps dropping well below freezing.