The monsoon also complicates transportation with roads and trails washing out while unpaved roads and airstrips may become unusable and cloud cover reduces safety margins for aviation. Rains diminish in September and generally end by mid-October, ushering in generally cool, clear, and dry weather, as well as the most relaxed and jovial period in Nepal. By this time, the harvest is completed and people are in a festive mood. The two largest and most important Hindu festivals—Dashain and Tihar (Dipawali)—arrive during this period, about one month apart. The post-monsoon season lasts until about December.