You can trek during all the year, depending on the region. Nepal has enormous temperature variability due to large altitude variations. The lowland plateau is subtropical (600-1200 m), the hills are dry (1200-2100 m) and the cold (2100-3300 m) and the high mountains are Alpine (3300-5000 m) and Tundra (5000-8848 m). Nepal is regarded best trekking season from Mid-September to mid-December.
The flowering plants, lush vegetation, and dazzling mountains make spring (Mar-May) trekking an outstanding setting. Spring looks like pleasure with singing birds, lovely views, and plenty of wildflowers. At lower elevation, the weather will be mild but cold at higher elevations. Mornings are typically crystal-clear in spring. But clouds carry rain showers in the afternoon.
In summer season (Jun-Aug) mornings in the afternoons and evenings are gloomy with rain. Trekking is very distressing, as the trail is muddy, slippery, and infested with leech. You are at risk of injury in wet weather. Additionally, natural disasters are more likely to occur; usually landslides in the hilly areas. You shouldn’t forget to bring insect repellants while you’re trekking. Himalayan regions would have a temperature of 16 to 20 degrees Celsius, hilly regions 20 to 30 degrees Celsius, and plain regions 34 to 39 degrees Celsius. While this isn’t a great trekking season, summer is better for forest botanists and research and higher altitudes. However, places such as Manang, Mustang, and Dolpo are in a shadow of rain. For these regions, summer is a good time. Temperatures are mild and it’s not that tough weather.
Autumn (Sep-Nov) is regarded as the best trekking season in Nepal. You will see great mountains, green hills, and an outstanding climate. Climate is typically clear, with medium to warm days and chilly nights. Natural event risks drop, making trekking a decent season and Nepalese Dashain and Tihar festivals are held during this season.
The Himalayan region freezes and snowfalls in winter Season (Dec-Feb). Trekking can be difficult in the higher elevations as snow may fill the route. You should walk under 3000 m in the winter. The Himalayan region temperature will be as high as -18 degrees Celsius, hilly regions 0 to 5 degrees Celsius, but in plain regions 10 to 15 degrees Celsius