NEW DELHI: A supergiant layer of fog enveloped north India and adjoining areas on Tuesday morning.
Spread across nearly 10 lakh sq km from Pakistan to the edge of Assam, the contiguous blanket of fog covered four countries and at least 13 Indian states, causing zero visibility and “severe cold day” conditions at many places in the region.
Experts said such massive fog formation usually happens once in three to five years, with the last such event having taken place in the winter of 2019-20, during the most prolonged spell of fog in recent times. Tuesday’s fog cover had a three times larger spread than the most widespread event during the last fog spell from December 18 to 28, which peaked on December 27.
The India Meteorological Department released an INSAT 3DR image taken at 8.45am on Tuesday, which shows fog and low-cloud-cover across the region, including parts of Pakistan, Nepal and Bangladesh, and spreading to areas in Madhya Pradesh, Chhattisgarh and Odisha in central India.
Under its influence, severe cold day conditions were observed over most pockets of Punjab and several places in Haryana, Chandigarh, Uttar Pradesh and Bihar. Cold day conditions persisted at some areas of Delhi and isolated spots in Rajasthan and Madhya Pradesh.
“Such a massive fog event has a cascading effect, with day temperatures plunging over a huge area and impacting a large population. Besides, low-visibility conditions create hazards for road, rail and air traffic,” said R K Jenamani, senior IMD scientist.
As per IMD data, the day temperature in Amritsar, Punjab, stayed at 9.5 degrees Celsius, 8.5 notches below normal. In west UP, Bareilly reported a maximum temperature of 10.6 degrees C while Bahraich in east UP reported 11 degrees C. The maximum at Patna was 7.5 notches below normal at 14.5 degrees C.
The minimum temperature in Churu, Rajasthan, fell below freezing at -0.9 degrees C, making it the coldest place in the northern plains.
Jenamani said such widespread fog usually occurs during period of prolonged absence of active western disturbance (WD) in north India. The northern plains haven’t been impacted by an active WD since October.
“Apart from absence of a WD, we need light or calm wind conditions and presence of moisture across a large area for such massive fog formation. On Tuesday, we saw an elongated line of subsidence of air which caused atmospheric inversion to take place over a huge area,” he said.
The IMD has warned that foggy conditions are likely to persist over the region in the next four days, with gradual reduction in intensity.