Geographically, Bhutan is a land of dramatic contrast.  From the near tropical southern border with India, steep slopes climb to snow-capped heights of over 24,750 feet / 7,500m at the northern border with Tibet.  Consequently, temperatures vary greatly between day and night and at different altitudes, so layered clothing for changing conditions, is recommended. In the central valleys, the summer rains are not as heavy as in the south and occur mostly in late afternoon and at night.  From mid-May to the end of September, the weather is warm at night (60-64F/17-18C) and in the day (72-78F/22-26C).  In winter, the sky is bright and it is sunny but cold, especially when the sun hides behind the mountains in the mornings and evenings.  At night, the temperature falls below zero.  Spring and Autumn are very pleasant with warm days and cool nights.