Many visitors, particularly from out of state, are not acclimated to the high elevations found on Rollins Pass. The lower atmospheric pressure (40 percent lower on the summit when compared to sea level) can cause altitude sickness, rapid dehydration, and if ignored can progress to high-altitude pulmonary or cerebral edema. Unexpected summer storms with violent lightning or sudden blizzards can also surprise tourists, who lose all sense of scale above timberline.