What are Western Disturbances?

Q. Why is this in news ?
A. With the approaching winter, minimum temperatures in the national capital have trended downward over the last due to the arrival of northwesterly winds called Western Disturbances.

Q. What is Western Disturbances? 

• A western disturbance is an extratropical storm originating in the Mediterranean region that brings sudden winter rain to the northwestern parts of the Indian subcontinent.
• It is a non-monsoonal precipitation pattern driven by the westerlies.
• The moisture in these storms usually originates over the Mediterranean Sea, the Caspian Sea and the Black Sea.
• Extratropical storms are global phenomena with moisture usually carried in the upper atmosphere, unlike their tropical counterparts where the moisture is carried in the lower atmosphere.
• In the case of the Indian subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.
• Western disturbances are more frequent and strong in the winter season.

Q. What is its significance? 

• Western disturbances, specifically the ones in winter, bring moderate to heavy rain in low-lying areas and heavy snow to mountainous areas of the Indian Subcontinent.
• They are the cause of most winter and pre-monsoon season rainfall across northwest India.
• Precipitation during the winter season has great importance in agriculture, particularly for the rabi crops.
• Wheat among them is one of the most important crops, which helps to meet India’s food security. An average of four to five western disturbances forms during the winter season.