Western Disturbances develop in the mid latitude region (north of the Tropic of Cancer), not in the tropical region, therefore they are called as mid latitude storms or extra-tropical storms.
Extra-Tropical Cyclones are also called as winter storms and blizzards.Western Disturbances are low pressure systems, embedded in western winds (westerlies) that flow from west to the east.It is a term coined by an Indian Meteorologist for the weather phenomenon which is propagated from the West.
The phrase Western Disturbance was first used in a published literature in 1947. However, its precursor Winter Disturbance was coined earlier in 1931
Impact:
In winter, western winds bring moderate to heavy rain in low lying areas and heavy snow to mountainous areas of the Indian subcontinent.
- India is a rain dependent country and while the south west monsoon covers most of India, parts of North India don’t get much rain from it. These regions depend upon snow and rain from western disturbance during winter season from November to March.
- Precipitation during the winter season has great importance in agriculture particularly for rabi crops including wheat, which is one of the most important Indian crops.
- They start declining after winter. During the summer months of April and May, they move across North India and at times help in the activation of monsoon in certain parts of northwest India.
- During the monsoon season, western disturbances may occasionally cause dense clouding and heavy precipitation.
- Western Disturbances are the cause of the most winter and pre-monsoon season rainfall across North-West India. This phenomenon is usually associated with cloudy sky, higher night temperatures and unusual rain. It is estimated that India gets close to 5-10% of its total annual rainfall from western disturbances.
- Weak western disturbances are associated with crop failure and water problems across north India.
- Strong western disturbances can help residents, farmers and governments avoid many of the problems associated with water scarcity.