The average and minimum temperatures differ among Russian regions. Winter is most severe in hinterland Yakutia (where no major armed conflicts happened to date), with the lowest temperature about −65°C. In European Russia (west of the Ural mountains), where most battles were fought, the average winter temperature is rarely below −20°C, but varies greatly: for example, temperatures in the winter of 2005/2006 fell to −20°C or −30°C in Moscow. In Russia this phenomenon is known as "Epiphany frosts" (крещенские морозы, Russian pronunciation: [krʲeˈɕɕenskʲije moˈrozɨ] - referred to Orthodox Epiphany on January 15), known for centuries for its low temperatures. But most recent winters in central Russia were unusually warm. A New Year's day without snow in Moscow and temperatures up to 10°C in the middle of winter are no longer rare.
Nevertheless, one factor for Russia's temperature is its Continental climate. The other is the geography of Russia: it is as far north as Canada, but has little open inland water to store the sun's energy. For example, in the Altai region in August, the temperature is above 20°C during the day, but at night can fall as low as −5°C.
Medieval Russians used skis to ease transport in their winter campaigns.Since it follows the autumn rasputitsa (nearly as troublesome), the severity of Russian winter is often linked to Russian military victories. In the Great Northern War, Charles XII of Sweden invaded the Russia of Peter the Great in 1707. The Russians retreated, adopting a scorched-earth policy. This winter was the most brutal of the 18th century, so severe that the salt water port of Venice froze. Charles' 35,000 troops were crippled, and by spring only 19,000 were left. The Battle of Poltava in 1709 sealed the end of the Swedish Empire.
Charles Minard's graph showing the strength of the Grande Armée as it marched to Moscow and back, with temperature (in Réaumur) plotted on the lower graph for the return journey. –30 degrees Réaumur = –37.5 °C = –35.5 °Napoleon's Grande Armée of 610,000 men froze to death.
The Russian army retreated before the French and again burnt their crops and villages, denying the enemy their use. Napoleon's army was ultimately reduced to 100,000. His army suffered further, even more disastrous losses on the retreat from Moscow.
According to an American military study, the main body of Napoleon's Grande Armée, initially at least 378,000 strong, "diminished by half during the first eight weeks of his invasion, before the major battle of the campaign. This decrease was partly due to garrisoning supply centres, but disease, desertions, and casualties sustained in various minor actions caused thousands of losses.
At Borodino on 7 September 1812—the only major engagement fought in Russia—Napoleon could muster no more than 135,000 troops and he lost at least 30,000 of them to gain a narrow and Pyrrhic victory almost 600 miles inside hostile territory. The sequels were his uncontested and self-defeating occupation of Moscow and his humiliating retreat, which began on 19 October, before the first severe frosts later that month and the first snow on 5 November."
During WWII the only cold winter was in 1941-1942, and the Wehrmacht lacked necessary supplies, such as winter uniforms, due to the many delays in the German army's movements. Hitler's plans for Operation Barbarossa also miscarried before the onset of severe winter weather: he was so confident of a quick victory that he did not prepare for even the possibility of winter warfare in Russia. Yet his eastern army suffered more than 734,000 casualties (about 23% of its average strength of 3,200,000) during the first five months of the invasion. On 27 November 1941, General Eduard Wagner, the Quartermaster General of the German Army, reported that
"We are at the end of our resources in both personnel and materiel. We are about to be confronted with the dangers of deep winter."