Large deficits (75-plus per cent) in winter snowfall have been reported across the northern regions of Ladakh, Jammu & Kashmir, Himachal Pradesh, and Uttarakhand throughout December 2023 and January 2024 since the westerly jet stream, which brings in the weather-making western disturbances, was located north of its usual position. 

This anomalous situation could be attributed to unusually high sea-surface temperatures in the North Atlantic Ocean since May 2023 and the melting of the Arctic Sea ice, according to Murari Lal, Technical Head (Climate Change) at RMSI, the Noida-based firm providing geospatial technology solutions, modelling, analytics, and IT consultancy services.

Extended snow, rain?

“Interestingly, this year’s snowfall in the Himalayas started in late-January and could contribute to ‘late winter’ and ‘extended seasonal snow and rains’ in the foothills of the Himalayas until March–May,” Lal wrote to businessline. Unprecedented heatwave conditions are anticipated across Odisha, Andhra Pradesh, Madhya Pradesh, and Bihar during April-June.

Western disturbances are synoptic-scale extra-tropical storms that originate in the Mediterranean region and move eastward, embedded in a sub-tropical westerly jet stream. They cause winter snowfall over Hindukush Himalayas in North India, which replenishes the glaciers in the region, Lal explains.

These storms are responsible for most of the winter precipitation in north India, which is crucial for the cultivation of the Rabi crop, and for the extreme precipitation events in the hilly terrains, which can lead to local flooding and avalanches. These are an important agent of the hydrological cycle, being responsible for most non-monsoonal precipitation.

Decline in frequency

Studies show that the past few decades have witnessed a significant decline in the frequency of western disturbances, total precipitation (due to decreasing intensity), and days with heavy precipitation over North India. Moreover, these disturbances have been twice as common in June in the last 20 years than during the previous 50 years. This is attributed to the delayed northward retreat of the sub-tropical jet, which historically has occurred before the onset of the summer monsoon in India.

Could delay monsoon

Lal suspects that El Niño conditions in the Equatorial Pacific could also interplay with sea-surface temperatures in the Atlantic and Indian Ocean, and with the summer monsoon circulation over India in such a way that the summer monsoon gets delayed, likely bringing to bear widespread drought conditions in some parts of India. 

On Thursday morning, the first of the back-to-back western disturbances was poised to enter South-West Rajasthan, breaking a lean cycle so far during this winter. It has spun up an induced cyclonic circulation (offspring circulation that accompanies an active western disturbance) over Central Pakistan and adjoining Rajasthan, as was projected in these columns a few days ago.

Rain, snow for hills

India Meteorological Department (IMD) said this would trigger light to moderate to fairly widespread to widespread rainfall or snowfall very likely over Jammu, Kashmir, Ladakh, Himachal Pradesh and Uttarakhand during next four days before tapering out. Isolated heavy rainfall/snowfall is likely over Kashmir valley, Himachal Pradesh and Uttarakhand on Thursday.

Light to moderate scattered to fairly widespread rainfall is forecast over Punjab, Chandigarh, Haryana, Delhi while it will be isolated to scattered over Uttar Pradesh, East Rajasthan on Thursday. Light isolated rainfall is very likely over the above regions on Saturday and Sunday. Isolated hailstorm is likely over Uttarakhand. 

Gusty surface winds

Moderate to intense thunderstorms and lightning and winds with speeds reaching 30-40 km/hr, gusting to 50 km/hr, are likely over parts of Jammu-Kashmir-Ladakh, Himachal Pradesh, Punjab, Haryana, Chandigarh, Delhi and West Uttar Pradesh on Thursday. Strong and chilly surface winds of the order of 30-40 km/hr may prevail over Punjab and Haryana, Chandigarh and Delhi.

Towards East India, light to moderate scattered to fairly widespread rainfall or snowfall is forecast over Arunachal Pradesh during the next seven days and isolated to scattered rainfall over West Bengal, Sikkim, Assam, Meghalaya and Nagaland, Mizoram, Manipur and Tripura on Thursday and Friday. Isolated heavy rainfall or snowfall is likely over Arunachal Pradesh on Friday. Isolated hailstorms may roll out over Arunachal Pradesh on Thursday, and the hills of West Bengal and Sikkim on Friday.