Western Disturbances

Western disturbances are eastward-moving extra-tropical weather systems that bring winter precipitation to northwestern India. They generally originate near the Mediterranean region and reach India through West Asia under the influence of the subtropical westerly circulation.

Movement and weather mechanism

These systems commonly approach India during winter as troughs or cyclonic circulations embedded in the westerlies. Their interaction with moisture and the barrier of the western Himalayas produces cloudiness and precipitation.

• An approaching disturbance often increases cloud cover and raises minimum temperatures by reducing night-time loss of heat.
• Its passage can be followed by colder northwesterly winds, clearer skies and a fall in temperature.

Rainfall and snowfall pattern

Western disturbances cause light to moderate winter rain over Punjab, Haryana, Rajasthan, Delhi and western Uttar Pradesh, while producing snowfall over the western Himalayan region.

• They account for much of the limited winter precipitation received by northwestern India.
• Strong disturbances may produce heavy rain, heavy snowfall, hailstorms or avalanches and can disrupt transport and daily life.
• Added moisture, low temperatures and weak winds may support fog, while rain and stronger winds can temporarily remove atmospheric pollutants.

Agricultural significance

Their winter rainfall, traditionally called mahawat in parts of northwestern India, supplies soil moisture needed by rabi crops.

• Moderate and well-timed rainfall benefits crops such as wheat and mustard, especially in rain-fed areas.
• Excessive rain, hail or unseasonal precipitation can damage standing crops and reduce yields.