We recently reported about bird migration to Yunnan. Mainly birds from Sibiria come to Yunnan during the winter months. In most parts of Yunnan it is definitely warmer than in Sibiria but also here it is advisable to protect oneself agains the chill, especially in higher elevation.
The highest mountains and the coldest temperatures in winter can be experienced in the northern part of Yunnan which borders Tibet. Meili Snow Mountain, the highest peak of Yunnan for instance, is maybe not the best place to visit during winter months unless you like climbing up snow and ice. In general, visits to Deqin County and also Shangri-La can end up in snowy weather and slippery roads. Also cancelled flights approaching this area over 3300m are not rare between December and February.
The further south one is heading, the warmer it gets; and that not only because of the direction (south) but also due to less elevation. While Dali and Kunming in central Yunnan are still located on about 1900-2000 meters, Xishuangbanna, bordering Myanmar and Laos, is a low, warm and sub-tropical winter get-away.
Another place worth visiting during the winter months are the UNESCO rated Yuanyang Rice Terraces (see movie here): while the mountains (about a 6 hour drive south of Kunming) still rise up to 3000 meters here as well, the rice fields are completely filled with water before fresh rice grows again in spring. The fields along the mountain sides offer spectacular views especially during sunrise and sunset when sky and sun are reflecting in millions of 'mirrors'.
Winter months in Yunnan are usually sunny and dry so the hard part of a winter - humid cold - is very rare. It is so sunny, that even strawberries in greenhouses ripen perfectly.
Check out our climate tables for weather information in various cities over Yunnan.