Mongolia is known as the "Land of Blue Skies," and with good reason: there are about 250 sunny days throughout each year, so good sunglasses are necessary.
The weather is bitterly cold during the winter, dropping down to -30º C in some parts. The weather during the summer varies from aimag to aimag, but it is generally hot. Outside of the Gobi desert, this time of year is marked with rains in some areas and cold nights.
Although most travellers choose to come to Mongolia between May and September, with the highest tourist peak in July during the Naadam holiday, other seasons can also be excellent for travelling. For the culture and the beauty of nature without crowds, shoulder seasons from March to May and September to November are best. October is a very good time to visit, and November is not too late to travel to Mongolia. It is still warm during the days but chilly at nights.
For visitors not afraid of cold, travelling to Mongolia from November till the Lunar New Year is still an option. Winter tourism is a developing area of the Mongolian tourism industry. The most rewarding experience will be visiting the nomads, and observing singing, dancing, wrestling and winter horse racing during "Tsagaan Sar", the traditional (Lunar) New Year celebration.