CLIMATE
The climate of Mount Everest is naturally extreme. In January, the coldest month, the summit temperature averages -36° C (-33° F) and can drop as low as -60° C (-76° F). In July, the warmest month, the average summit temperature is -19° C (-2° F). At no time of the year does the temperature on the summit rise above freezing. In winter and spring the prevailing westerly wind blows against the peak and around the summit. Moisture-laden air rises from the south slopes of the Himalayas and condenses into a white, pennant-shaped cloud pointing east; this “flag cloud” sometimes enables climbers to predict storms. When the wind reaches 80 km/h (50 mph), the flag cloud is at a right angle to the peak. When the wind is weaker, the cloud tilts up; when it is stronger, the flag tilts down.
From June through September the mountain is in the grip of the Indian monsoon, during which wind and precipitation blow in from the Indian Ocean. Masses of clouds and violent snowstorms are common during this time. From November to February, in the dead of winter, the global southwest-flowing jet stream moves in from the north, beating the summit with winds of hurricane force that may reach more than 285 km/h (177 mph). Even during the pre- and post-monsoon climbing seasons, strong winds may arise suddenly. When such storms develop, sand and small stones carried aloft, as well as beating snow and ice, pose problems for climbers.
Precipitation falls mostly during the monsoon season, while winter storms between December and March account for the rest. Unexpected storms, however, can drop up to 3 m (10 ft) of snow on unsuspecting climbers and mountain hikers.
Base Camp, which serves as a resting area and base of operations for climbers organizing their attempts for the summit, is located on the Khumbu glacier at an elevation of 5,400 m (17,600 ft); it receives an average of 450 mm (18 in) of precipitation a year.
From June through September the mountain is in the grip of the Indian monsoon, during which wind and precipitation blow in from the Indian Ocean. Masses of clouds and violent snowstorms are common during this time. From November to February, in the dead of winter, the global southwest-flowing jet stream moves in from the north, beating the summit with winds of hurricane force that may reach more than 285 km/h (177 mph). Even during the pre- and post-monsoon climbing seasons, strong winds may arise suddenly. When such storms develop, sand and small stones carried aloft, as well as beating snow and ice, pose problems for climbers.
Precipitation falls mostly during the monsoon season, while winter storms between December and March account for the rest. Unexpected storms, however, can drop up to 3 m (10 ft) of snow on unsuspecting climbers and mountain hikers.
Base Camp, which serves as a resting area and base of operations for climbers organizing their attempts for the summit, is located on the Khumbu glacier at an elevation of 5,400 m (17,600 ft); it receives an average of 450 mm (18 in) of precipitation a year.
