Mt. Everest base camp trek is a heavenly paradise in Sagarmatha National Park in Nepal. It is the tallest mountain in the world and the weather forecast around there is very unpredictable. A trek to Everest base camp starts at an altitude variation from 2800m to 5545m. Nepal experiences four seasons as below
Autumn (Late September to November): This season is right after the Monsoon and all the haze goes down and the views are as clear as crystal. This is the ideal time of the year to travel in Nepal. All the visibility is clear and calm. The daytime temperature reaches up 12 degrees centigrade and nighttime temperatures drop down to 2 degrees centigrade in the months of September and October. November will be colder than the previous month.
Winter season (December to February): The winter season is freezing cold and some of the settlements from the upper part of the Everest trek area move down to Lukla and below. The daytime temperature will be about -8 to -10 and night time will be -12 to -18 degrees centigrade. However, there are still few people on this trek. In my experience, winter is better for the EBC trek due to a smaller number of people, clear visibility, and great opportunity to see Ghoral, Musk Deer, wild Goat, and diverse flora and fauna. If you are okay with cold then plan your trek to EBC in winter.
Spring (March to May): Spring reminds another big season for trekking in Nepal. The temperature remains moderates 17 degrees centigrade during the day time and cool during the night time. Having little to no rain and thunder and snowfall are common during the spring season. Another good thing to do this season is meet with Everest climbers at base camp and have a nice chat with tea/coffee.
Monsoon Season (Jun to Mid-September): This is a rainy season in Nepal. It rains heavily and leads to mudslides and flooding. But in higher altitudes above 4,000m, there is very little to no rain. In the Monson season, the visibility is poor, and cloudy skies. The average temperature is moderate like 10 to 18 degrees centigrade and rainfall is about 450 mm.