Mongolia is an extremely dry, cold country. It averages 257 cloudless days a year. The north has the highest amount of precipitation with about 20 to 35 centimeters a year. The precipitation is lowest in the south, which gets about 10 to 20 centimeters a year. In the extreme south is the Gobi desert. Some parts of the Gobi receive little to no precipitation in most years. The average temperatures in the majority of Mongolia are below freezing from November through March and are about freezing in April through October. Common January and February temperature averages are -4 degrees Fahrenheit and -40 degrees during winter nights. Extreme summer highs can reach 100 Fahrenheit in the Gobi and 91 degrees in Ulaanbaatar, Mongolia's capital city. Frost covers more than half the country for the majority of the year. This makes construction, roadbuilding, and mining difficult. All rivers and freshwater lakes freeze over in the winter, and some small streams freeze through to the bottom during the cold season. The summer in most of Mongolia is mild, but in the Gobi Desert, it can reach up to over 100 degrees during the day.