What are Western Disturbances

In News: The India Meteorological Department (IMD) has said that due to intense western disturbance, Jammu and Kashmir, Himachal Pradesh and Uttarakhand are likely to receive moderate rainfall and snowfall in the next few days.

What are Western Disturbances (WDs)?

• About: WDs are extratropical storms that originate in the Mediterranean region and bring sudden winter rain to the north-western parts of the Indian subcontinent.
• Origin:  WDs originate in the Caspian Sea or the Mediterranean Sea as extra-tropical cyclones.
• Travelling path: They gradually travel across the middle-east from Iran, Afghanistan and Pakistan to enter the Indian sub-continent.
• Important characteristics:
  • They are a non-monsoonal precipitation pattern which is driven by the westerlies.
  • These extra-tropical storms are a global phenomenon. They may happen during any season, not necessarily in monsoon.
  • This phenomenon usually carries moisture in the upper layer of the atmosphere, unlike their tropical counterparts where the moisture is carried in the lower layer of the atmosphere.
  • The western disturbances are embedded in the mid-latitude subtropical westerly jet stream.
  • They travel at speeds up to 12 m/s (43 km/h; 27 mph).
• The meteorological phenomenon that is similar to WDs:
  • Nor’easters: These storms occur along the northeastern coast of North America and can bring heavy precipitation, strong winds, and coastal flooding.
  • European windstorms: These storms are common in Europe and can bring strong winds and heavy precipitation, particularly to the western and northern parts of the continent.
  • Mesoscale Convective Systems (MCS): These are characterized by a complex of thunderstorms that normally persist for several hours or more, and commonly found in the central and eastern parts of North America, South America, Africa, and Asia.

Western Disturbances Source

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