The weather in Everest Base Camp trek is always unpredictable because the weather condition switches in every 15 minutes. Normally, the weather is fairly perfect in the morning and get worse in the afternoon. The evenings and the nights are very cold on the trek. If you do Everest Base Camp Trek during Autumn( Sep-Nov) and Spring ( Mar-May), you will have incredibly good weather. In summer ( Jun-Aug), you will have rain and in winter ( Dec-Feb) you will have snow.