Explain western disturbances.
We can define Western Disturbance as “a low pressure area or a trough over surface or the upper-air in the westerly winds regime, north of 20°N, causing changes in pressure, wind pattern and temperature fields. It is accompanied by cloudiness, with or without precipitation.” The term Western Disturbance (WD) was coined by Indian meteorologists for describing the systems moving from the west to east direction. WDs originate in the Caspian Sea or the Mediterranean Sea as extra-tropical cyclones. They gradually travel across the middle-east from Iran, Afghanistan and Pakistan to enter the Indian sub-continent.
Though WDs move across the Indian region throughout the year, they are in their peak during winter months of January and February. Their effect is minimal during the monsoon months in India.Western Disturbances along with their induced systems are the principle rain producing systems during non-monsoonal months over Northwest India including Punjab, Haryana, Uttar Pradesh and Delhi. Their effect sometime extends up to Gangetic plains and Northeast India. They are also responsible for bringing snowfall in the higher reaches of Jammu & Kashmir, Himachal Pradesh and Uttarakhand.