Western Disturbances:
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Western Disturbance (WD), labelled as an extra-tropical storm originating in the Mediterranean, is an area of low pressure that brings sudden showers, snow and fog in northwest India.
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The disturbance travels from the “western” to the eastern direction.
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These travel eastwards on high-altitude westerly jet streams – massive ribbons of fast winds traversing the earth from west to east.
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Disturbance means an area of “disturbed” or reduced air pressure.
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In the term “extra-tropical storm”, storm refers to low pressure. “Extra-tropical” means outside the tropics. As the WD originates outside the tropical region, the word “extra-tropical” has been associated with them.
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A WD is associated with rainfall, snowfall and fog in northern India.
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It arrives with rain and snow in Pakistan and northern India.
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The moisture which WDs carry with them comes from the Mediterranean Sea and/or from the Atlantic Ocean.
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WD brings winter and pre-monsoon rain and is important for the development of the Rabi crop in the Northern subcontinent.
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The WDs are not always the harbingers of good weather.
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Sometimes WDs can cause extreme weather events like floods, flash floods, landslides, dust storms, hail storms and cold waves killing people, destroying infrastructure and impacting livelihoods.
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Expert opinion on western disturbances is divided regarding the 2013 floods in Uttarakhand in which over 5000 people were killed, after three days of incessant rainfall.
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Western disturbances are more frequent and strong in the winter season.