The weather and climate can vary depending on the region of Nepal you are visiting. However, day temperature in southern part of Nepal such as in Chitwan, Lumbini, goes over 35 degree Celsius in the months of Apr, May, Jun, Jul, Aug with occasional rain and goes near 0 degree Celsius during the months of Nov, Dec, Jan, Feb. In the mountains and hills temperature remains below 30 degree Celsius in the summer but goes below 0 in the winter.
The key to comfort in packing the right clothes to Nepal lies in layers. Whether chilly, wet, hot or cold, wear comfortable layers that you can peel off and put on should the weather change. Be sure to pack a good pair of comfortable shoes or hikers with good traction that will be fitting for exploring the outdoors.