Due to the apparent northward movement of the Sun temperature start rising from March, toward the end of the May a low-pressure trough is developed which extends from the Thar Desert in the northwest to the Chotanagpur plateau in the east. In the heart of this low pressure through in the North West, dry and hot winds blow in the afternoon. These hot and dry winds are locally known as Loo. Dust storms in the evening very common during May in the northwestern part of the country. Sometimes they are accompanied by light rains and pleas and cool breeze which give temporary relief from the oppressive heat. Pre-monsoon showers in Karnataka and Kerala that help in the ripening of mangoes are also called"Mango Showers". Deficiency of these rains affects the mango harvest in South India. In the eastern and North-Eastern parts of the subcontinent, violent thunderstorms at a speed of about 60 km to 80 km per hour are experienced. Their direction is mainly from the North-West; hence they are called the Norwesters. These storms are accompanied by heavy showers and hails.