Mongolia has extremely continental climate with long, cold winters and short summers. The country averages 257 cloudless days a year, and it is usually at the centre of a region of high atmospheric pressure. Precipitation is highest in the north, which averages 200 to 350 mm per year, and lowest in the south, which receives 100 to 200 mm. The extreme south is the Gobi, some regions of the Gobi receives no precipitation at all in most years. The name Gobi is a Mongol word meaning desert, depression, salty marsh, or steppe, but which usually refers to a category of arid rangeland with insufficient vegetation to support marmots but with enough to support camels. Gobi rangelands are fragile and are easily destroyed by overgrazing, which results in expansion of the true desert, a stony waste where not even Bactrian camels can survive.
Average temperatures over most of the country are below freezing from November through March and are about freezing in April and October. January and February averages of −20 °C are common, with winter nights of −40 °C occurring most years. Summer extremes reach as high as 38 °C in the southern Gobi region and 33 °C in Ulaanbaatar. Most of Mongolia is covered by perma frost (grading to continuous at high altitudes), which makes construction, road building, and mining difficult. All rivers and freshwater lakes freeze over in the winter, and smaller streams commonly freeze to the bottom. Ulaanbaatar lies at 1,351m above sea level in the valley of the Tuul River. Located in the relatively well-watered north, it receives an annual average of 310 mm of precipitation, almost all of which falls in July and in August. Ulaanbaatar has an average annual temperature of −2.9 °C and a frost-free period extending on the average from mid-June to late August.