Dense fog blankets Indo-Gangetic plains; more in store, warns IMD

A large patch of dense fog shrouded the entire Indo-Gangetic plains on Sunday morning, stretching from Pakistan in the west right up to the Bay of Bengal in the east, satellite images provided by India Meteorological Department (IMD) showed.
“Due to a passing western disturbance, there has been some moisture incursion. Conditions are already very cool and the winds are calm. These are perfect conditions for dense fog to develop. Moreover, there are no strong winds or no such weather system likely immediately that can clear this layer of fog. Unless there is a very active western disturbance this layer will remain. Another western disturbance is expected around January 16 and 17 which may help to an extent,” said DS Pai, senior scientist, IMD.
Also read- Flight disruptions in Delhi amidst thick fog: 10 diversions, over 100 delays
The India Meteorological Department (IMD) defines “shallow” fog in a region when visibility drops to 500-1,000m, “moderate” fog when visibility is 200-500m, “dense” fog when visibility is 50-200m, and “very dense” when visibility dips to 50m or lower.
On Sunday, Delhi recorded dense fog for more than seven hours — between 3am and 10.30am — leading to the diversion of 20 flights at the Indira Gandhi International airport, while at least 400 more flights were delayed. The fog led to the season’s coldest minimum of 3.5°C. However, the Capital logged a few hours of sunshine, resulting in a maximum of 20.6°C — one degree above normal for this time of the year, and the first time that the day’s high has been above the 20-degree mark.
Cold wave to severe cold wave conditions prevailed in many places of Punjab and Haryana. Cold wave conditions prevailed in some parts of Delhi and in isolated pockets of west Uttar Pradesh. Dense to very dense fog was also reported in most parts of Punjab, Haryana, Chandigarh, and Delhi.
IMD defines a “cold day” when the maximum is at least 4.5°C below normal, even as the minimum is below 10°C. This classification is upgraded to “severe” when the maximum drops 6.5°C below normal. The Met department defines a “cold wave” in a region where the minimum temperature is 4.5°C or more below the normal mark, or when it drops to 4°C or lower.
“Cloudy or foggy conditions do not allow the absorption of solar radiation. Without the sun’s heat reaching the ground, the days are very cold. There is an incursion of cold air from the northwest, which is also leading to very cold nights, so both maximum and minimum temperatures are low,” said Pai.
Also read- Delhi fog: Consider these ‘safety tips’ if you are travelling by road
Dense to very dense fog, and cold days and nights are likely to continue over parts of northwest India — including Delhi, Punjab and Haryana — for at least three more days, IMD has warned.
Dense to very dense fog conditions are also likely to prevail in isolated pockets of Jammu, Himachal Pradesh, and Uttarakhand till January 16. Cold day to severe cold day conditions are likely to continue in parts of Punjab, Haryana, and Chandigarh till January 16, and in isolated pockets till January 17, IMD said.
Cold wave conditions are very likely in isolated pockets of Uttar Pradesh and north Rajasthan on January 14 and 15, the department said, while ground frost conditions are also likely over northwest India on January 14 and 15.
In peninsular India, the northeast monsoon rains from Sunday ceased over Kerala-Mahe, south interior Karnataka, Tamil Nadu-Puducherry-Karaikal, Rayalaseema, and adjoining areas of coastal Andhra Pradesh and Yanam, indicating a change in season. There has been no rainfall activity over the southeast peninsular region during the past two days. Water vapor imagery indicates dry air prevailing over the region at middle and upper tropospheric levels. In the lower levels, dry winds from northern India are prevailing over the region.