Glacier's geography, straddling the Continental Divide, sets the stage for clashes of two very different climates. Warm, wet Pacific air moves in from the west, and cold dry Arctic air from the northeast. They meet at the Divide. The western valleys generally receive the most rainfall, but daytime temperatures can exceed 90 degrees F. Strong winds and sunny days often predominate on the east side of the park.
In the driest corners of the park, along the northeast and northwest edges, rainfall averages 23 inches (58.4 cm) a year, while in the lowlands of the west side, about 30 inches (76.2 cm) of precipitation fall in the average year. As moist air is forced up to the elevations of the Divide, it loses its moisture and precipitation jumps to 100 inches (2.5 m) or more in isolated mountain cirques. Snowfall settles to around a 16-foot (4.9 m) average snowpack. Early summer snow removal on Going-to-the-Sun Road, which crosses the Continental Divide, is so spectacular it has become a spectator sport (via Road Crew photos in the park flickr album).
The east side of Glacier is in a rain shadow and gets less overall precipitation than the west. The dryness of the east side is also due to high winds. Downslope winds are often 50 mph or more, sometimes reaching 100 mph. Warm chinook ("snow-eater") winter winds regularly create a temporary spring, raising temperatures over 30 degrees in just minutes. If the cold Arctic air pools deep enough on the east side, spills over the top, and collides with Pacific moisture, raging blizzards can result. One dumped 44 inches (1.1 m) of snow in a day.
Scientists stationed at Glacier are doing landmark research on the effects of global climate change in this mountain ecosystem. While precipitation changes are more difficult to predict than temperature, scientists expect to see more precipitation fall as rain (rather than snow) with a warming climate. This means snowpacks may not be as deep in the future.