For the most part of the year, the region of Nathula experiences extreme cold weather and the condition gets even worse in winters due to heavy snowfalls. The summer is indeed the best time to explore the heights of the Nathula pass.
In summers, i.e. from March to May, the temperature is comparatively milder with brighter sunshine. The temperature does not exceed 15 degree C but the nights are still colder, hence woolens are always recommended.
Winters are extreme colder in Nathula and the mercury may drops down to -25 degree C during December and January. The lakes get completely frozen and the entire region experiences heavy snowfall. Though the place looks extremely bewitching due to white snow shining everywhere but during winters, the pass is generally banned for the tourists.