Although Tibetans refer to their country as Gangs-ljongs or Kha-ba-can (“Land of Snows”), the climate is generally dry, and most of Tibet receives only 18 inches (460 millimetres) of rain and snow annually. The Himalayas act as a barrier to the monsoon (rain-bearing) winds from the south, and precipitation decreases from south to north. The perpetual snow line lies at about 16,000 feet in the Himalayas but rises to about 20,000 feet in the northern mountains. Humidity is low, and fog is practically nonexistent.
Temperatures in the higher altitudes are cold, but the lower valleys and the southeast are mild and pleasant. Seasonal variation is minimal, and the greatest temperature differences occur during a 24-hour period. Lhasa, which lies at an elevation of 11,830 feet, has a maximum daily temperature of 85° F (30° C) and a minimum of −2° F (−19° C). The bitterly cold temperatures of the early morning and night are aggravated by the gale winds that blow throughout most of the year. Because of the cool dry air, grain can be safely stored for 50 to 60 years, dried raw meat and butter can be preserved for more than one year, and epidemics are rare.