The climate in the Himalayas is dependent upon two factors: altitude and time of year. The annual summer monsoon usually begins in June and ends by late September. The dry season lasts from October through May. Spring and autumn are the best trekking seasons. 
 
For the trekking in Nepal October and November, temperatures are relatively moderate and skies are usually brilliantly clear. AS a general guideline, daytime temperatures at altitudes of around 3040 m to 3654m can range between 8 C to 18 C, and night time temperatures between -12 C and 1 C. Rain or snow is possible. 
 
December is one of the coldest months in Nepal, but the skies are very clear. Daytime temperatures can range between 4.5 C and 12.7 C; nighttime temperatures can drop between – 17 C and – 4 C. with possibility of snow. Winter is a good time for trekking at elevations below 3957m. Its too cold for high altitude treks and winter snows often close the high passes. 
 
The months of March, April and May bring a beautiful profusion of spring wildflowers (Nepal’s famous rhododendron forests are in bloom at this time at lower altitudes). Daytime temperatures are slightly warmer than in the fall, ranging between 10 C and 22 C, while at night temperatures can drop to between –6 C and  
7 C