Western Disturbance that brought rains over Delhi unique in many ways

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Did you know that the Western Disturbance that brought in record rainfall over Delhi these last three days is unique in many ways?

Persistent rainfall since Friday night broke a record or two for highest rainfall for January on Saturday.

Palam observatory had recorded 47.6 mm rainfall for the 24 hours ending at 8.30 a.m. on Saturday, which the India Meteorological Department (IMD) said, was the second highest for data between 1959 till 2022 for the month of January.

As IMD had predicted beforehand, it was the Western Disturbance that had brought in copious amounts of rainfall over not just Delhi-NCR but across northwest India.

The IMD has on Sunday said the high moisture feeding from Arabian Sea over northwest India has cut off, which will lead to dry weather, even when it may be cloudy, over Punjab, Haryana, Delhi NCR and adjoining West Uttar Pradesh from Monday onwards. IMD also said that scattered light / moderate rainfall / snowfall would continue till January 11 over Western Himalayan region due to remnant moisture.

So, what was so unique about this time’s Western disturbances (WD)? And before that, what is WD?

WDs are more frequent and stronger in the winter season. IMD terms WD as the extra-tropical storm that originates in India’s west side, unlike most of the rain giving systems that come to India from eastern side. WD originates all the way in the Mediterranean Sea and Caspian Sea region and is the reason for rainfall in winters in northwest India and also adjoining parts in Pakistan.

Most of the time, the rainfall, and snowfall in the Himalayas, is restricted to Jammu and Kashmir, Punjab, Haryana, Delhi, and Rajasthan, which may extend to Madhya Pradesh, as happened this year. But sometimes, a stronger WD also extends all the way up to Uttar Pradesh, Bihar, West Bengal, and of course, parts of Nepal.

On an average, there are six to seven disturbances per month moving across India during the winter.

According to senior scientists from the IMD, R.K. Jenamani: “The uniqueness of this WD is that it caused some record rains, prolonged spell of drizzle and clouding, and also brought some parity to temperatures of both day and night over Delhi and adjoining areas of northwest India from the night of January 7 till evening of January 9.”

Jenamani explained the three important features that the vertical extent of the system was well upto upper troposphere upto 9,000-10,000 metres height; it remained stationary over north Pakistan & neighbourhood for almost 36-48 hours from January 7 night till January 9 evening and at lower and middle level, its tail end interacted with lower level tropical easterly, resulting very high moisture feeding from the Arabian Sea and thus sustained such longer spell of precipitation and over such a large areas of NW India and central India.

Indeed, the heavy rains have caused a lot of damage to rabi crops in Madhya Pradesh and at least 22 tourists froze to death in Murree in northern Pakistan due to excessive snowfall.

“Under the impact from this very intense WD, Delhi’s Safdarjung has created another record besides yesterday’s record rainfall. January 2022 rainfall till January 9 evening has been recorded as 63.6 mm, which is already highest in the last 26 years after January 1995. The January 1995 rain was recorded as 69.8 mm.”

This WD also brought in another feature. The difference of maximum and minimum temperature for January 7 evening till January 9 evening, called diurnal variation, also for two days remained the same, uniquely at 1.2 degrees Celsius.

Maximum temperature between January 7-8 was 16.4 degrees Celsius while the minimum temperature was 15 degrees Celsius. Similarly, for January 8-9, the maximum temperature was 15.2 degrees Celsius, and the minimum was 13.8 degrees Celsius.

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